Conservative leader Kemi Badenoch is set to challenge Sir Keir Starmer by directing her MPs to oppose the proposed cuts to sickness welfare.
The Conservatives will team up with Labour rebels in a bid to defeat the package, which is expected to shave £5billion off the bloated benefits bill.
Approximately 100 Labour MPs have penned a letter to Sir Keir, expressing their intent not to back his proposed cuts when the vote arises in Parliament later this month.
The PM has a working majority of 165, while the Tories have 120 MPs.
It means that if the Conservatives team up with a large band of Labour rebels they could inflict a defeat.
The Tories will oppose the plans on the basis that the cuts do not go far enough.
A government source said: “We could lose the vote if the Tories team up with Labour MPs to vote against the measures.
“The rebellion is expected to be intense, with some MPs likely to be in tears. It could foster significant resentment towards No10 and might even lead to a lasting division.”
Work and Pensions Secretary Liz Kendall has claimed the reforms will get more people into work and protect the benefits system.
Speaking earlier this month, she said: “Unless we reform the system to help those who can work to do so, unless we get social security spending on a more sustainable footing . . .the risk is the welfare state won’t be there for people who really need it in future.”
Britain’s welfare bill has ballooned since Covid.
According to official estimates, taxpayers will have to pay a staggering £70billion a year on working-age sickness and disability benefits by 2030.
