More than 100 Labour MPs have signed their names to a Commons bid to halt the Government’s welfare reforms in their tracks, enough to threaten Sir Keir Starmer’s majority.

Some 108 MPs’ signatures appear on a reasoned amendment declining to give the welfare reform Bill a second reading when it returns to the Commons on July 1.

The rebellion, the Prime Minister’s largest yet, would be enough to defeat the Government’s plans if opposition MPs joined the Labour rebels.

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

But it calls for the Commons to decline to continue scrutinising the Universal Credit and Personal Independence Payment Bill “because 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”.

There has been no formal consultation with disabled people who will be impacted by the changes, the MPs said.

They also point to the fact that an analysis of the impact of the reforms on employment from the Office for Budget Responsibility will not be published until the autumn.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).

Ministers have previously said the reforms could save up to £5 billion a year.

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.

He added: “You’re right to point out that this phrase reasoned amendment isn’t just a small tweak. It would stop the legislative process if it succeeded.”

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.

Shadow foreign secretary Dame Priti Patel, meanwhile, would not say whether the Conservatives would side with the Labour rebels in the Commons.

But she told Sky News the Tories backed the “fundamental principle of welfare reform, which could lead to structural changes in our country which our economy needs”.

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.

“This is the better future we seek to build for our constituents and our country.”