Labour would fight a snap general election vowing to press ahead with Brexit, but it would secure better terms, John McDonnell has said, defying demands from party members to include a second-referendum pledge in any manifesto.

The standoff between Theresa May and the EU27 leaders in Salzburg this week, and the apparent lack of a parliamentary majority for her Chequers plan for Brexit, have raised the possibility of an early general election.

Labour has repeatedly made clear that it would prefer this option over a “people’s vote” on any deal.

The shadow chancellor also suggested on Saturday that the rail industry could be renationalised within five years under a Labour government.

He told BBC Radio 4’s Today programme it would be possible to bring all franchises back under public control during a single term in office, amid reports he is planning a public ownership unit within the Treasury to deal with renationalisations.

Earlier, speaking as Labour prepares to gather in Liverpool for its annual conference, with Brexit high on the agenda, the shadow chancellor told the Guardian he would expect his party’s stance to be similar to the one it took in 2017.

“We would be in the same situation there, where we would be saying: we’re accepting that original vote; this is the sort of deal that we want,” McDonnell said.

“I really think people want this sorted. That means negotiating a deal that will meet people’s objectives. So you don’t get hung up on the semantics; you do the deal that will protect their jobs, and address some of the concerns that they had during the referendum.”

He underlined his scepticism about the idea of a vote on the final deal, which will be discussed in Liverpool after more than a hundred constituency Labour parties, and the Labour-supporting unions, called for it to be put on the agenda.

“The debate around the next manifesto will go on, but I really worry about another referendum,” he said.

“I’m desperately trying to avoid any rise of xenophobia that happened last time around; I’m desperately trying to avoid giving any opportunity to Ukip or the far right. I think there’s the real risk of that. We’re not ruling out a people’s vote, but there’s a real risk, and I think people need to take that into account when we’re arguing for one.”

Much of Labour’s manifesto, if there was a snap poll, would probably be based on last year’s document, The Many, Not the Few, drafted by Corbyn’s policy chief, Andrew Fisher. But the final version would have to be approved by a committee of senior party figures at a so-called clause V meeting – and would be expected to take party conference resolutions into account.

Advocates of a people’s vote would like to see Labour shift its position decisively towards advocating a poll on whatever deal is struck with Brussels.

But McDonnell’s words echoed those of Corbyn, who told BBC Scotland on Thursday, when he was asked whether Brexit should go ahead: “The referendum made that decision.”

Labour is keen not to be blown off course by Brexit, and hopes instead to use its conference to show that it is preparing for government, and translating last year’s popular manifesto into concrete policies.

McDonnell told the Guardian he would set up a public ownership unit inside the Treasury, allowing him to personally oversee one of Labour’s most transformative economic policies: the nationalisation of public utilities.

Labour has said it will bring water, rail and the Royal Mail back into public ownership and examine whether private finance initiative (PFI) contracts can be brought back on to the Treasury’s books.

McDonnell would direct the unit to examine whether consumers, workers and the local community could take on part-ownership and it would be overseen by a public and community ownership advisory board, made up of trade unions, business leaders and civil society members.

McDonnell said: “The reason for being transparent about how we’re doing it is to reassure people, this is the mechanism we’re going to use to do it. We’ll bring the expertise in, we’ll work up as much as we possibly can before we go into government, but these are the papers that we’ll give the civil servants in the run-up to the election.”

McDonnell has been holding regular meetings with City figures in a bid to convince them Labour’s economic policies should not be cause for alarm. He was cheered by a recent article by former Tory minister and Goldman Sachs economist Lord O’Neill saying the party had “stepped into the vacuum left by the government and appears to be offering the radical change that people seek”.

And McDonnell is acutely conscious that Labour would be unlikely to be given much of a honeymoon by instinctively sceptical financial markets, so it would have to move rapidly to convince voters it could make their lives better.

“I’ve been saying to Jeremy and the others, the first Queen’s speech has got to be incredibly popular. It’s got to change people’s lives, quickly and effectively, so that means putting money back in people’s pockets through the real living wage, rolling out the investment quickly. And the public ownership alongside that will assist us, because it will mean that we’re not wasting resources on profiteers.”

Corbyn’s longtime political ally has adopted a markedly higher profile in recent months, in particular since the antisemitism row that preoccupied senior Labour figures for much of the summer.

“It was horrible and it was heart-rending,” he says now. “I had no summer at all, but we came out of it. As soon as we get back into the swing of things, we just want to get out there, get the policies out there, and get round as much media as we can.”

The charm offensive has reignited speculation that he covets the leadership for himself, if Corbyn decided to step aside – or he could even elbow his old ally aside. But asked if he wants to be Labour leader, he says: “No, no, no, no, no. And as I said the other day, the next leader’s going to have to be a woman.

“Every year, it’s a hardy perennial, it’s either I’m plotting or I’m holding Jeremy Corbyn hostage so he won’t resign. We’ve worked together nearly 40 years. You can’t get much greater in terms of solidarity and loyalty between us. We’re mates, we’re close friends, we agree. We have disagreements on tactics, on minor things, but we resolve it in private by the end of the day.”