MPs will vote next week on welfare cuts aimed at disabled people, Prime Minister Sir Keir Starmer and Deputy Leader Angela Rayner pledged today.

Playing a game of chicken with the growing number of Labour rebels prepared to defy the government on the issue, Sir Keir pledged to press ahead with his savage cuts.

One Labour MP described it as a “charge of the political light brigade” by Blairite budgetary hardliners.

But Sir Keir told LBC radio that “there’ll be a vote on Tuesday, we’re going to make sure we reform the welfare system,” while Ms Rayner told MPs  simply: “We will go ahead on Tuesday.”

This does not mean that the debate will definitely proceed as planned, only that Downing Street has not yet made a final determination.

The number of Labour MPs prepared to back an amendment which would end all progress on the Bill has risen to over 120.

This would mean that Sir Keir could only prevail with Tory support.  

Conservative leader Kemi Badenoch is flirting with backing the government, but is demanding a pledge of no tax increases in the autumn Budget in return, something no government could offer while retaining any self-respect.

Sir Keir now faces several choices, all damaging to his political future.

He could postpone the vote, despite his pledges to press ahead. This would be as good as an admission of defeat, and would only postpone the moment of decision.

Or he could press ahead and bid to scrape through with Tory Party support, a ruinous position for any Labour prime minister, which would leave him forever tainted.

He could meet Labour rebels’ concerns and change the content of the proposals, which, coming soon after a U-turn on the winter fuel benefit cut, would shred his credibility.

Finally, he could decline to make concessions to either the Conservatives or the Labour left but thereby risk losing the vote and his remaining authority.

Ministers and others have been ringing rebels, warning that a defeat for the government could mean either a general election, which would likely see Labour decimated, or at least the resignation of the Prime Minister.

The latter threat has not had the impact anticipated, since the number of backbenchers happy to contemplate a change of leadership is growing as Labour’s poll numbers sink.

Among those backing the Labour rebels are London Mayor Sadiq Khan and Greater Manchester Mayor Andy Burnham, both of whom are believed to have their eyes on the top job eventually.

Mr Burnham said: “When the Parliamentary Labour Party delivers its collective wisdom in such numbers, it is invariably right. And it is right on this.  

“I would say to the government, listen to the PLP.”

Mr Khan likewise said that ministers “must urgently think again” about the plans, while Labour Wales First Minister Eluned Morgan has also called for a rethink.

PCS union general secretary Fran Heathcote wrote to MPs urging them to join the rebellion.

“I very much hope you will vote against these ill-thought-out proposals which will do nothing to create a fairer, more effective social security system and are neither in the interests of our members administering the system, nor of disabled people,” she wrote.

The Bill aims to save £5 billion to help fund Labour’s war drive by restricting eligibility for the personal independence payment, the main disability payment in England, and limiting the sickness-related element of universal credit.

A Downing Street spokesman insisted that opposition to the reforms was “not progressive or moral.” 

Speaking at the Nato summit in The Hague, Sir Keir claimed that the system stopped people getting into work.

“So we have to reform it, and that is a Labour argument, it’s a progressive argument,” he said.

Challenged in a Commons committee as to the government’s failure to consult with disabled people’s organisations, welfare minister Stephen Timms claimed that the urgency of the escalating benefits bill made such niceties impossible.