Jeremy Corbyn has suffered a double blow after a fourth Labour MP resigned her post in protest over his reshuffle, and one of the party’s own whips criticised the sackings of “authentic, working-class voices” from the Shadow Cabinet.

Alison McGovern, the chair of the Blairite campaign group Progress, has quit from her position running John McDonnell’s economic policy review into how to reduce child poverty and boost low incomes.

Her resignation comes after three shadow ministers, Jonathan Reynolds, Stephen Doughty and Kevan Jones, resigned on Wednesday in protest at the sackings of Pat McFadden and Michael Dugher from Mr Corbyn’s front bench.

The discontent over Mr Corbyn’s leadership shows no sign of being stemmed. Party whips are normally the enforcers of loyalty, but, speaking to The Independent on Sunday, the Labour whip Conor McGinn said: “I wasn’t surprised that Pat and Michael were sacked. They are authentic, working-class, traditional Labour voices. Sadly, those seem to be getting fewer and fewer. If we aren’t careful, Labour will completely lose touch with the people we are supposed to represent.”

Ms McGovern’s resignation from her policy role was prompted by claims from John McDonnell, the shadow Chancellor, that the three MPs who quit as ministers were a “right-wing clique” who did not represent the party and had coordinated their resignations to inflict maximum damage on Labour. He also said her campaign group Progress, to which the MPs belonged, was pursuing a “right-wing, conservative agenda” and was “hard right”.

Ms McGovern yesterday hit out at Mr McDonnell’s accusation, saying he had “stepped over [the] line”.

“We all misspeak when we are tired – but he went on to repeat this disappointing slur as he toured the media studios in an attempt to defend the messy and divisive reshuffle he has been helping to organise,” she said. “He clearly meant it and, as shadow Chancellor, he should know better.”

A friend of Ms McGovern said she had tried to work for the new Labour leadership. “John McDonnell wasn’t Alison’s choice, but she knuckled down and agreed to chair the review for John because she’s a party loyalist. She respected the members’ decision and she wanted to do everything she could to make it work.

“Members voted for Jeremy but they did not vote for John McDonnell to smear people who have devoted their lives to the party as ‘conservatives’ or the ‘hard right’.”

However, Mr Corbyn’s aides insisted that he has emerged from the reshuffle in a stronger position, having removed his most ardent opponents on the Labour front bench and asserted his authority over Hilary Benn, the shadow Foreign Secretary.

Critics hit out at the reasons given for sacking or demoting shadow ministers in the reshuffle. Mr Dugher said the Labour leader had told him that he had been sacked because he “didn’t like things I’d been writing”. Mr Dugher said he had only written “in defence of good colleagues and the new politics”.

Mr McFadden was given a six-point dossier of disloyalty, including a question in the Commons in which he stressed that IS alone was responsible for the deaths in Paris – and the West was not to blame.