The combative response from the Jeremy Corbyn-backing organisation comes as both Labour and the Conservatives remain braced for further walkouts with the turbulence at Westminster showing no sign of abating.
The Labour leader himself has described the decision of his eight former colleagues as “disappointing” and called on them to face the electorate in by-elections.
But following the MPs’ refusals to call such votes, Momentum will hold mass canvassing events in Streatham, Stockport and Penistone, and Stocksbridge – the constituencies of ex-Labour MPs Chuka Umunna, Anne Coffey and Angela Smith.
The action aims to build support among voters in each area for a by-election and raise awareness that their local MP no longer represents the Labour Party.
Momentum added that in the hours after the surprise press conference of MPs – announcing their decision to leave Labour and delivering withering criticism of Mr Corbyn’s leadership – the group raised more than £15,000 in donations from its members.
Laura Parker, the national coordinator at Momentum, said constituents had voted for a Labour MP at the 2017 snap general election for “a Labour MP standing on a Labour manifesto”.
“Now they’ve left the party and joined a Blairite-Tory coalition standing on a completely different platform,” she said. “This is not what their constituents voted for. The only fair and decent thing to do is give their constituents a choice and call a by-election.”
Ms Parker continued: “Polls show the vast majority of Labour voters back the party and the policies, not individual candidates. These splinter group MPs ran in 2017 on a manifesto of public ownership, scrapping tuition fees and ending austerity.
“Now they’re working hand in hand with the Tories they’ll revert back to an agenda of privatisation, deregulation and tax cuts for the wealthy.
“This is unfair, undemocratic and dishonest. If they care about their constituents rather than their own careers they should step down and fight a by-election.”
In retaliation to the splinter group, Labour called on Wednesday for greater power for voters to trigger by-elections if their MP defects from the political party whose banner they were elected under.
Under current legislation, such proceedings can only go ahead under certain circumstances, such as an MP receiving a jail sentence or a breach of parliamentary standards.
Shadow cabinet minister Jon Trickett said: “Power comes from the people but for too long the overwhelming majority have been shut out. That’s why trust in politics and elites is rightly falling.”
He continued: “Communities should not have to wait for up to five years to act if they feel their MP is not properly representing their interests, especially with the Fixed Term Parliament Act.
“This proposed reform has the dramatic potential to empower citizens and will be one of many measures the Labour Party is planning to consult on and announce that will change the way politics in this country is done.”
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