Former shadow chancellor John McDonnell has accused the Labour leadership of allowing a “right-wing faction” to become “drunk with power” and attempt to “destroy” the left of the party.
The backbench MP has written to party leader Sir Keir Starmer to complain that dissenting voices are being stifled and warning such an approach will weaken the Opposition.
Mr McDonnell told BBC Newsnight: “Under Tony Blair we didn’t have mass expulsions like this or anything like that.
“We didn’t have the withdrawal of the whip unless it was something very extreme. There was an atmosphere of tolerance but actually respect as well.”
It is the latest flare-up of a factionalism row within Labour, with Corbyn-era figure Mr McDonnell using some of his strongest language yet to rebuke the leadership.
Party leaders have been accused of trying to squeeze out left-wing voices in recent months, including the serving North of Tyne mayor Jamie Driscoll, who has been described as “the last Corbynista in power”.
Mr Driscoll was blocked from standing for another role in the North East after sharing a platform with filmmaker Ken Loach, who was expelled amid efforts to root out antisemitism from the party.
Mr McDonnell also criticised Labour last week after it was accused of moving to potentially suspend a prominent member over a tweet that appeared to endorse the benefits of cross-party cooperation.
Neal Lawson, chief executive of the centre-left Compass think tank, claimed that he faced expulsion after 44 years of membership.
Labour dismissed any suggestion he had been ousted as “false” but said he had been served with a “notice of allegation” for allegedly expressing support for another party.
Mr Lawson told Newsnight: “It’s worrying when it reaches the soft left. I’m just a pluralist, I like working with people across the Labour Party and outside of the party… if they come for me I’m not sure who’s safe.”
Mr McDonnell said: “I think what he’s (Sir Keir) allowed to happen is a right-wing faction become drunk with power and use devices within the party almost on a search and destroy of the left.
“They seem to be more interested in destroying the presence of the left of the party than in getting a Labour government.”
A Labour spokesperson said: “The public need to know that if someone is a Labour candidate that is a mark of quality they can rely on. It’s absolutely right that we have high standards for those who are going to represent the Labour Party at election time.
“This is a changed Labour Party back in the service of working people so we can build a better Britain.”
