John McDonnell has accused members of Labour’s national executive committee of attempting to rig the leadership contest by changing the rules to prevent more than 130,000 new members from voting.

The shadow chancellor, one of Jeremy Corbyn’s closest allies, said there was “widespread concern and anger” about the decision that only people who had joined the party before January this year could participate in the forthcoming leadership contest.

Speaking to the Guardian, he added: “And the decision to increase the fee to become a registered supporter from £3 last year to £25 this year -; and to leave just 48 hours in which to sign up -; both discriminates against the low waged, unemployed, students and the elderly and is an affront to Labour values.

“These decisions, taken by Labour’s national executive committee [NEC] this week, will be widely seen at best as turning our back on an open participatory party democracy, and at worst as an attempt to gerrymander and rig the leadership election.”

McDonnell said the huge increase in members in recent weeks, thought to be mainly from people who want to back Corbyn, ought to be a cause for celebration. To “lock those members out of the right to vote” was a step backwards for Labour and a step backwards from party democracy, he added.

Regardless of any legal action that may be taken, the national executive needs to think again and reset rules for the contest that makes this leadership election the most open and democratic the party has ever held,” McDonnell said.

He added he was deeply concerned that members had not been consulted before the NEC decided to ban all local party meetings. “This is of particular concern over the next few months and sends a negative signal to the membership.

Anushka Asthana Political editor Guardian, Friday 15 July 2016