A damning verdict on the Government’s cuts to disability benefits has been published by more than 100 Labour rebels who are threatening to humiliate Prime Minister Sir Keir Starmer by voting down his plans. The numbers are high enough to defeat the Government in a vote on July 1, as Sir Keir faces his biggest rebellion since becoming Prime Minister.

An amendment signed by 108 Labour MPs states: “The Government’s own impact assessment estimates that 250,000 people will be pushed into poverty as a result of these provisions, including 50,000 children.” They are furious over proposals announced by Work and Pensions Secretary Liz Kendall making it harder to claim Personal Independence Payment (PIP), which helps disabled people with living costs. Ministers want 800,000 people lose an average of £4,500 annually and in addition, changes to Universal Credit are expected to see an estimated 2.25 million current recipients of the health element impacted, with an average loss of £500 per year.

The number of Labour rebels is high enough that Sir Keir and Ms Kendall would face defeat if Conservative and other opposition MPs join forces with them. It would leave a £5 billion black hole in the Government’s spending plans, as money it hoped to save by cutting benefits would need to be found elsewhere.

The amendment, published on Tuesday’s order paper, notes there is a “need for the reform of the social security system”.

But it rejects the Government’s Universal Credit and Personal Independence Payment Bill and points out there has been no formal consultation with disabled people who will be impacted by the changes, the MPs said.

It also says an analysis of the impact of the reforms on employment from the Office for Budget Responsibility will not be published until the autumn.

Several Labour select committee chairs were among those who put their name to the amendment, including chairwoman of the Treasury committee Dame Meg Hillier, and Debbie Abrahams, chairwoman of the work and pensions select committee.

The MPs who signed the amendment “want the Government to listen and to think again on this Bill”, Ms Abrahams said.

She added: “We are being asked to vote for this Bill before disabled people have been consulted, before impact assessments have been conducted and before we have given enough time to some of the Government’s key policies – investing in the NHS, to the right to try, and to work coaching – (to) have been able to bed in.”

Vicky Foxcroft, the former Government whip who resigned over the welfare plans, has also signed the amendment.

Commons Speaker Sir Lindsay Hoyle would need to select the amendment when MPs debate the legislation at its second reading.

Under the proposals in the Bill, ministers will limit eligibility for the personal independence payment (Pip), the main disability payment in England, and limit the sickness-related element of Universal Credit (UC).

Amid the growing threat of rebellion, Cabinet Office minister Pat McFadden warned on Tuesday morning it would be a “very serious thing” for Labour MPs to effectively vote down the Bill at its first major outing in the Commons.

Mr McFadden insisted the growing costs of welfare were unsustainable, as a “city the size of Leicester” was being added to the population on benefits each year.

“I don’t think as the party of labour, the party of work, we can sit back and be relaxed about so many people going on to long-term sickness and disability benefits,” he added.

If defeat seems like a real possibility then one option for the Government would be to withdraw the Bill and prevent a vote taking place in a humiliating climbdown.

Work and Pensions Secretary Liz Kendall spent Monday night speaking to backbench MPs about the reforms at a meeting of the Parliamentary Labour Party (PLP).

Those leaving the meeting insisted there was broad consensus in the room, with only few MPs standing up to make their opposition known.

The Work and Pensions Secretary told the PLP that the plans are “rooted in fairness”.

She argued they are about ensuring the survival of the welfare state so there is always a safety net for those in need of it.

Ms Kendall added: “Above all, they are about our belief that everyone can fulfil their potential and live their hopes and dreams when, collectively, we provide them with real opportunities and support.