He laughs heartily when I tell him I was shocked by these latest revelations. After all, this comes on top of the same newspaper headlining one article on the Monday after Jeremy Corbyn appointed McDonnell to his shadow cabinet with ‘Corbyn has just appointed a nutjob as shadow chancellor’, albeit the paper did later apologise and changed the header online to ‘man from cloud cuckoo land’.

The media in general has taken agin McDonnell. It has described him variously as one of the ‘loony left’ and as ‘the most controversial figure in the Labour Party’ after claims emerged suggesting that he had been an IRA sympathiser and had threatened to kill Margaret Thatcher.

He was already being painted as one of the most divisive characters in Corbyn’s shadow cabinet -; there were predictions of all-out civil war over his appointment -; and this even before he said he would “swim through vomit” to vote against the Conservative’s Welfare Bill and had thrown a copy of Mao Tse-tung’s ‘Little Red Book’ across the Commons in his idiosyncratic reply to George Osborne’s Autumn Statement.

When I interviewed McDonnell nine years ago, during his abortive attempt to push Brown into a leadership contest and out from a simple coronation to be the next leader of the Labour Party, he had struck me then as a man of great integrity. Yes, he was opposed to New Labour spin and remained steadfastly true to his socialist beliefs. But he seemed far removed from the left-wing firebrand that the red-tops tried to portray.

He may have since, infamously, been suspended from the House of Commons for five days after grabbing the ceremonial mace during a heated debate on the Heathrow airport expansion plan in 2009, but he struck me then as more a man at peace than at war. And he laughed -; a lot -; often at his own expense. I liked that.

So what’s gone wrong? What has life thrown at him in those intervening years that has exposed this thinking man of the far left as a batterer of bobbies? He laughs uproariously and then explains that during the 1980s, when he was chair of the finance committee in Ken Livingstone’s GLC, he had been walking through Parliament Square en route to County Hall to present his budget, when he passed a group of Greenham Common Women who were getting arrested for singing.

There was one woman, who was a legal observer, and she was taking names and as she got arrested she passed the pen and paper to him and he was then subsequently arrested, charged, thrown in a police cell and taken to court the next day.

“I think I was charged with GBH,” he says. “In court, three officers all gave evidence saying I jumped on the back of a police officer and hit him. Well, Paul Boateng, Lord Boateng as he now is, was representing me and an American tourist comes forward with a cine camera -; that’s how old this all is -; and the film showed I was actually just walking by.”

What, no vaulting of security barriers? No jumping on the back of a police officer and no knocking nine bells out of him?

“No,” he laughs. “I was just walking by. The film showed that. The case was dismissed and there was some small compensation that I think went to a charity or something. To cut a very long story short, I was on the stage at the TUC conference in Brighton last month and Yanis Varoufakis [the former Greek finance minister] was there and he had just described how he was radicalised in Great Britain in the 1980s by the protests of the Greenham Common Women and I stood up and said, ‘I can tell you a funny story about that’ and of course the Telegraph, who must have had a journalist there, then ran the story that you’re talking about saying ‘McDonnell boasts about assaulting a police officer’.

“At the very end of the story, there was a line saying the case was dismissed. Not only did I not do it but the funniest thing about it was that when I got arrested for it, my brother was a police officer. He was a policeman for 35 years and absolutely dedicated to the service.

“When the Queen visited his area he was in the protection unit and he had been a hostage negotiator and yet it was the police that fitted me up. He couldn’t believe it. Neither could I and ever since then I have always taken individual cases like the Guildford Four and others up because I was so shocked that this could happen to someone like me who was innocent. It was shocking and I know that people in the street might say that this kind of thing could never happen or there’s no smoke without fire, but I was a parliamentary candidate, I hadn’t done anything and that could have destroyed me.

“The story the Telegraph ran was rubbish. But when this is happening all the time it is difficult to counter. You can do a rebuttal but then even a rebuttal becomes a story -; ‘John McDonnell denies assaulting a police officer’. It used to happen with Ken on the GLC all the time. He was The Sun’s ‘most odious man in Britain’ and then when people saw him on live media and he didn’t have two heads they would see he was alright. The same thing is happening to me now and yes, I recognise it was done to the likes of Nicola Sturgeon during the referendum and the general election time too. It’s tough.

“They’ve also chosen not to understand my humour and I have promised Jeremy Corbyn ‘no more jokes’ but I am a Scouser and you can’t help yourself. But one, the media distort it anyway; secondly, they sometimes don’t get it; and thirdly, I am sometimes a bit reckless so I have to behave myself.

“I just don’t think they [the media] get us or the new politics that is emerging. But we have taken a view that we will try and work with the media as best we can and to be fair, there is some that will give you a fair crack of the whip. But the written media, in England, in particular, is so rabidly anti-left or anti anything new and so rabidly conservative with a big and small ‘c’, it is difficult to break through.

“We have concentrated on the media that we can work with but, more importantly, the live media because it can’t be edited, misinterpreted or wilfully abused.”

If McDonnell is sounding paranoid, he probably has every reason.

“It is extraordinary the lengths some of the media have gone to. I have had a person from the Daily Mail camped in the constituency for a number of weeks now, touring round looking for what they would describe as dirt. All my family have been approached, some of whom I haven’t seen since the last wedding or the last funeral -; at least it’s putting us all in touch, so that’s good,” he adds with typical humour.

“What has been nice about it has been the support I have had in the local community. I think we have cut through by using live media and social media and by showing we are not unprofessional. However, we are swimming against the tide: one, they oppose our politics and with the Murdoch media, with all due respect, that is entirely understandable; but two, they just don’t understand the nature of the new politics and the new politics is much more engaged. And what I find interesting now is that more and more people just don’t get their views from the written media anymore.”

Up until a few months ago, few people outwith the Labour Party, the political commentariat and trade union movement had heard of him. However, McDonnell has been involved in local London politics for at least 40 years, been an MP since 1997, and, interestingly, he and newly elected SNP MP Tommy Sheppard go back 40 years when they were both in local government in London together.

McDonnell was elected to the GLC at 29, was Ken Livingstone’s deputy, chair of the finance committee and credited with transforming Livingstone’s ‘Red Ken’ public profile into more that of a national treasure. Although they fell out after Livingstone accused McDonnell of manipulating figures for political purposes -; a claim completely refuted by McDonnell -; they have since reconciled.

As a backbench MP he was always on the left of the party; he was chair of the socialist Campaign Group, set up in Westminster by the late Tony Benn’s supporters in the 1980s, and has remained a loyal member since. He was unenamoured by New Labour and one of its fiercest critics, rebelling on votes with a frequency only matched by his closest parliamentary friend, Jeremy Corbyn. He has been a challenger in two of the more recent Labour leadership battles -; firstly when Brown stood and secondly against Ed Miliband -; but didn’t get much further than a name on the ballot paper.

When I asked him nine years ago what made him think that an unknown politician like him could possibly challenge an experienced politician like Brown, he rightly asked me if I had ever heard of Tony Blair before his surprise emergence? He also pointed out that at 29, he was the GLC deputy leader, chair of finance and ran a £3bn budget. Who, he asked me then, of the current or potential leaders had that kind of experience at the same point in their careers?

When Ed Miliband stood down after the general election, McDonnell was back on familiar ground -; how to open up debate about what the Labour Party stood for when it was the usual suspects that looked set to stand.

“I had wanted Ed to stay on for a bit so we could have a bit of an analysis. But when he did stand down, I gathered together all the left groups and tried to persuade people that there was no way we could run a candidate, that we basically had five years of work to consolidate the left for the future.

“I was looking forward to sliding into the role of elder statesmen of the left and then into retirement at some point, but then there was such overwhelming demand from the membership that we had to have a candidate. I convened a campaign group meeting and I said there was no way I was doing it. I had done it twice before and there was no way that I’d get on the ballot paper. Diane [Abbott] had done it but hadn’t been able to mobilise the vote and we all literally looked at Jeremy at the end of the table and said, ‘it’s your turn, mate’.

“It took us a week to get the nominations and in the final 10 seconds, I had four people lined up to nominate if he got to 34 and he was on 33 and I did this emotional appeal and two of them cracked and we got on the ballot paper and that was it.

“I thought we could get 25 to 30 per cent of the vote and no one believed me. So I was overwhelmed when I did see the scale of support right across the piece and it wasn’t just from the new £3 members but right across the membership. Halfway through I realised we were on to a winner.

“Jeremy wanted me to go out on the campaign trail with him and I said, ‘no way, it would look like a tour of Last of the Summer Wine’. I told him to just go out there and explain it himself in his own words.

“Our slogan was ‘honest politics, straight talking’ and I think his appeal was that we had had two decades, maybe more, of a synthetic-type politics and a plastic-type politician who would wait to see what the polls were saying before they said anything, whereas Jeremy was saying, ‘this is what I believe in’ and then asking people to tell him what they thought and he’d be asking questions and also coming up with ideas and he would say, ‘that’s not a bad idea’ and would take it away to work on. People just liked his honesty and integrity but also, most of the policies that came up we had a fairly straightforward solution so that people could understand.

“The media ignored us at first but then we got two thirds of the way through and Tony Blair intervened -; that had a very positive impact and then the media started thinking we could win so they started mobilising against us and there was yet another backlash and a firming up of our vote.

“Every time someone from the past like Blair or Brown intervened, our support went up. They should have just asked the question, what is motivating 1000 people to turn up to a hall and hear someone talk common sense? In Camden, we were at a huge hall that holds 2000 people and there were people queuing down the street and the Fire Brigades Union had to bring in a fire engine so Jeremy could address the street from the top of it. There’s a lovely film of two young people breaking into the hall for the political meeting. Have you ever heard anything like that, climbing in through a window to get in?”

Did the engagement seen during the Scottish referendum help mobilise support for Corbyn?

“I think that’s a really interesting question and I think the Scottish momentum of people getting engaged certainly infected what went on down here. But I just think the climate was right; people were so disillusioned with what was going on with politics and they also wanted a bit of hope.”

McDonnell is undoubtedly a conviction politician. You only need to look at his voting record: opposed the war in Iraq; voted against ID cards, the introduction of student top-up fees and of Blair’s anti-terror laws; he protested over an assortment of bills that held hints of any infringement of human rights; and on matters of immigration and asylum, he consistently voted against his own government. Now, some say his lack of party discipline will come back to haunt him.

We meet on the morning before the vote on bombing Syria. The media has given Corbyn a beating over his apparent swithering over whether to offer his MPs a free vote. The Metro headline even screeches that Corbyn, not David Cameron, has taken Britain to the brink of war. I ask McDonnell if he finds that ironic.

“You have to come to terms with the English media which is if Jeremy had successfully whipped the Labour Party into opposition to the war he would have been blamed by the English media for selling the country out. Jeremy, in terms of some elements of the media, cannot win, just cannot win, and this is not just the usual stuff of politicians bleating about the media -; we have never seen a media assault like this in our history.

“The reality of what has happened is that in the shadow cabinet itself, I think we are almost near a majority as not against bombing; in the Parliamentary Labour Party (PLP), there is certainly a majority and it could be quite sizeable; and in the constituency membership and in the trade unions, it is an overwhelming majority. But what we don’t have is a majority for whipping. And whipping would have been counterproductive because on issues like this Jeremy and I have been arguing for all the years we have been in parliament that they are matters of conscience, so it would have been contradictory for us to impose it and it wouldn’t have been sustainable.”

In the end, 66 Labour MPs -; 11 in the front bench -; voted with the Conservative Government for war and 153 voted against bombing. They were joined by seven Conservatives and all 54 of the SNP MPs. The vote was carried and bombs started dropping on Syria within hours.

The fallout for the Labour Party saw MPs like Yvette Cooper, Stella Creasy and Chuka Umunna, who all voted with the government, claim they were being insulted, trolled and threatened with deselection.

“The problem we have at the moment -; that we will get through -; is that it is a huge culture shock for the members of the PLP that all of a sudden we have a mass membership that is growing all the time and we are moving towards being more of a social movement than a traditional political party,” says McDonnell.

“The SNP has just such a disparate membership now and I agree with what you say that Nicola Sturgeon says, that there are no negatives to that increased membership, but you do have to manage it and you do have to establish mechanisms and processes to allow that to happen and even in establishing those processes people will feel vulnerable. So, for instance, when Jeremy wrote to all the members asking them what they thought about his position [on bombing Syria], some members of the PLP saw that as a threat. They thought that was a manoeuvre but it wasn’t -; it is just open politics.

“People in the PLP are faced with this very different movement and where there might have been 20 or 30 people turning up at a local constituency meeting, it is now 70, 80 or a 100 and local membership has increased from 400 to 1,000 or even quadrupled that. It is a culture shock and that is something that some have embraced and for others, it is a struggle.

“I keep saying to Jeremy that our job is to help smooth that path, which is why all this stuff about deselection is just rubbish. We are not doing deselection or reselection, we just want to make sure there is a smooth path from being a centralised hierarchical party to a social movement and that is what we are doing. In the meantime, you will have people going to the media saying there are plots and so on but that’s not the case.

“We are talking about a small number who are having a hard time coming to terms with it and I know there have been lots of reports about PLP meetings being really rough and all that but they haven’t been that rough. I did my thing on the economy the other Monday and had rounds of applause and all the rest of it, although not sure if I would after the Mao incident. That was my last joke, honestly.

“Look, on domestic politics, there is virtually nothing between us, absolutely nothing, other than some want to go faster than others. There’s nothing contentious but for two areas: Trident -; and that is coming up -; and foreign policy when it comes to decisions about war and peace. On everything else, there is not much between us. And what people are excited about is having to think about new ideas.

“When Jeremy set up the shadow cabinet, everyone was offered a job. But we had people refusing permission on jobs that weren’t even offered, on policies that they hadn’t even seen, so now we are settling down and I am going around everyone and saying, ‘do you want to come back and help us on such and such?’

“Chris Leslie, who was shadow chancellor, is now chair of the treasury back-bench committee and I have said to him that we have an open door here and we will meet every month. In addition, I have asked him to help us go through the line-by-line budget review and he has been nothing but helpful.

“I have started all these reviews and set up this economic advisory council with world leaders advising us. Today we are launching a review of the Treasury, and on the HMRC I have another group of real boffins -; accountants, auditors, you name them which is really very exciting no, no, seriously, it is very exciting -; looking at that and I’ve got Danny Blanchflower, or David as he is called, reviewing the Bank of England monetary policy.

“But I am also saying we need to look at the economy from another way and how it affects individual people in society so we have set up a group looking at the economy and women and Yvette [Cooper] is participating in that.

“I met with the City of London Corporation last week and given I’ve been threatening to abolish it for the last 30 years, that could’ve been difficult. I told them, still want to abolish you but let’s talk and see where we go from here. I said to Mark Boleat, who is chair of the Policy and Resources Committee there and who I have known for yonks because he chaired a charity in my area and we get on quite well, that what I want to do is bring my Treasury team down to the City Corporation and I want him to bring the City people in to us and we would have a day or two of acclimatisation and he said, ‘great, we’ll do that and we’ll work together because there is lots we can agree on’.

“When you look at the finance sector in particular, there are lots of allies there that will help us to do the reforms that we want. Every Thursday morning, Graham Turner, from GFC Economics [Turner was one of the first to predict the banking crisis and wrote the book The Credit Crunch] from the heart of the City, comes to give my team a detailed market analysis and to make sure all my Treasury team are up to speed with the economy and the City.”

So McDonnell does believe that the bankers do have a role to play?

“They have a role but they have to recognise their own significance as well and what I don’t understand is why they aren’t banging at the door of government a bit more. Take Harold Wilson’s days in government, he wasn’t just doing beer and sandwiches for trade unionists at Number 10, what he did have was key players round the table giving advice on the future economy and that’s what I want to get back to. And key players are the entrepreneurs themselves from every sector, including finance, the workers themselves but also those at the leading edge of new ideas, and I want to have them involved in a structural way in government.”

Should business be worried about McDonnell as a potential Chancellor?

“Well, of course, business is worried about me because they read the Times and the Telegraph. If I read about me in the Times and Telegraph I’d be worried about me too,” he laughs.

“What I am trying to do is just be straight with them and I’m doing a series of speeches at different venues, setting out what we are trying to do and where we are going. I did a speech at Imperial College last month and the reason I did it there was that they have this hub that mixes academia, science, research and development and companies, all on one site.

“I was saying to them that the future of our economy is based upon one, that we are the financial centre of Europe and we accept that, but two, that we have an unbalanced economy. So where do we go from here, where are the high wages and high skills? They are in new technology, so I want Britain to be that new technology centre of Europe so we need to invest, invest, invest.

“The wealth creators are the businesses, bankers and entrepreneurs but they are also the workers themselves and those in R&D, and none of those should be frightened of me because I am trying to bring them all together again. I am also trying to say that the reason we are in this mess at the moment, where we have this maldistribution of wealth, is because we are living on our past glories rather than to our future.

“Those wealth creators have no role in government anymore and the supply chain of ideas and advice, from the shop floor to government, has broken down and they need to be part of that discussion in terms of the future direction of our economy.

“We live in an incredibly unequal society and we need to tackle that. I talk of equality of outcome rather than equality of opportunity but I believe we can tackle some of the major inequalities quite quickly.”

And to do that you need to be an electable government. Is Corbyn’s shadow cabinet a future government?

“Oh yes,” he says without the hint of a smile. “I have bored the whatever off people on the left for years saying this is not about left adventurism. It is all very good making great speeches and all the rest of it but the serious on the left have to be serious about being in government tomorrow.

“You know, all the way through the Blair and Brown years, we were arguing about the nature of the policies that they were pursuing. I thought they would fail or not take us as far as we wanted to go and would ultimately fail for us electorally. I don’t know if this sounds pompous but we were proved right.

“All along, Jeremy, myself and others on the left, were swimming against a tide. We were marginalised, abused and trivialised but actually, much of what we said was right.

“Look at banking. I was the first MP to raise Northern Rock, others claim it, but I was the first to raise it and no one knew what I was even talking about and then when I raised the issue of Granite [a Jersey registered, special-purpose financing vehicle set up to allow the Northern Rock to sell off large parts of its mortgage book to bondholders] they all thought I was mad. But Granite was the offshore operation for Northern Rock for basically tax-avoidance schemes. We were well in advance in terms of these issues and that was because I was being briefed by people like Graham Turner and others in the City all along.

“Look at housing. That is one of the biggest issues we face in London and the south-east right now and as soon as I was elected in 1997, along with Jeremy, we led on behalf of the Campaign Group arguing for investment in housing. Gordon Brown agreed we should be investing in housing, but in repairs not building. That was our fatal mistake. We inherited a housing crisis from the Tories which we then exacerbated by not building.

“In my constituency tonight there will be 200 people who are living in B&Bs, which was meant to be illegal. They are living in squalid conditions. During the general election, people didn’t believe me when I told them how many people were living, literally, in sheds, like shanties, and so I went around taking photographs of them and it is appalling. This is the sixth richest country in the world and we have people living in sheds. I had a woman who came to my office because I have an open-door policy and she kissed my hand, begging for a property and I never want that to happen again. And this is solvable. Literally, in the lifetime of a parliament, I could resolve this by investing in housing.

“If families are not in a B&B they are in other temporary accommodation often with a buy-to-let landlord. And in my area, the buy-to-lets are the most neglected houses on the street and the kids in those properties are in there for maybe two years maximum and then kicked out. So there’s a constant churn. And if you come home from school and there’s nowhere to do your homework and your bedroom is overcrowded, where do you go, you go out on the street and you get caught up with a gang. It is destroying my community.

“That is just one consequence of two policy failures: not building enough homes and encouraging buy-to-lets by subsidising taxpayers to get into that regime. It is shocking.

“It’s got worse and the levels of inequality are staggering. You can see from Thatcher on, that whole 30 to 40 years of erosion of the public realm and it is manifesting itself in levels of poverty and the breakdown of community that I don’t think we have witnessed for a century.

“I have been talking to people about taking them to see these almost shanty towns and just as I am doing a tour of a lot of the new tech companies and back into the City, I have said, ‘why not come back with me to view some of the things I am trying to tackle?’ because it is remarkable how stratified society is now and how cut off from one another we are.

“You know me, you interviewed me nine years ago and I have always said that we, on the left, have to be in a situation where we have the policies and the ideas and the ability to take control the following day and if we don’t work on that basis, we will never be taken seriously. So I have always worked on the basis that no more left adventurism, no more flying kites.

“We are serious about seizing power and we are serious about the nature of politics, which is why every year in parliament I did an alternative budget to Brown and one of our city analysts said the other day that if we had followed my budget, we wouldn’t have been in the crisis that we were because we would have been in control of the finances.”

Does he still see hope?

“Oh yes, and if I can become shadow chancellor that should give hope to anyone,” he says, smiling broadly and breaking that recently made promise of ‘no more jokes’.