Kemi Badenoch said Keir Starmer isn't fit to govern the country as she lashed out at his "utter capitulation" over welfare. The Tory leader branded the reforms "pointless" after the Labour leader was hit by a major backbench rebellion.
Mrs Badenoch also blasted the Prime Minister's "shambolic" track record since entering No 10. Her onslaught came as the Prime Minister was forced into a second humiliating climbdown in a week, shelving controversial disability benefit reforms to stave off a backbench revolt.
Ministers have now scrapped plans to tighten rules for Personal Independence Payments (PIP) after furious backbenchers warned they would sink the Bill.
In the end, MPs voted the legislation through by a majority of 75, with 335 in favour and 260 against.
But the PM still suffered a damaging revolt, with 49 Labour MPs refusing to give the Bill a second reading.
It marks the biggest rebellion of Sir Keir's premiership so far - the sixth biggest Labour revolt in history - and heaps fresh pressure on his authority less than year into his premiership.
Mrs Badenoch said: "They should bin it, do their homework, and come back with something serious. Starmer cannot govern."
But Work and Pensions Secretary Liz Kendall insisted the Labour Party was "100%" behind the Prime Minister, but told broadcasters there were "lessons to be learned" after a major rebellion over welfare cuts.
The concessions will cause a major headache for Chancellor Rachel Reeves as the welfare squeeze was originally meant to save £4.8 billion a year, which was subsequently reduced to £2.3 billion when the Bill was first watered down last week.
Postponing any changes to the eligibility criteria for Pip means it is now uncertain how much the reforms will save from the soaring welfare bill.
Under the original proposals, claimants would have needed to score a minimum of four points - which measure how hard they find it to perform tasks unaided - in at least one daily activity to qualify for Pip from November 2026.
Currently they need to score eight points to qualify - but these can be spread over several tasks.
Sir Stephen Timms, the disability minister, had been set to publish a report at around the same time as the change was due to come into effect
But in a dramatic intervention in the Commons on the eve of the crunch welfare vote, Sir Stephen confirmed the findings of his review would come out before any changes to the Pip system were made.
It is no longer certain that the proposed change, which had sparked fury from Labour MPs, will ever be introduced.
Stuart Anderson, a Conservative MP, told Sir Stephen he was doing an "admirable" job of "defending the farcical".
Charlotte Gill, head of campaigns and public affairs at the MS Society, said: "We thought last week's so-called concessions were last minute. But these panicked 11th hour changes still don't fix a rushed, poorly thought-out Bill."
It is the latest humiliation for Sir Keir following a string of U-turns that has severely weakened his leadership.
Speaking earlier to the Daily Express on a day of heated drama in Westminster, Mrs Badenoch unleashed a savage attack on Sir Keir's first year as Prime Minister.
Describing it as an "absolute shambles", she said: "He may have been ready for an election. He was not ready for government. They made promises and they've broken them because they don't know how to run this country."
The Conservative leader pointed to a litany of "broken promises" on taxes, the winter fuel payment, a grooming gang enquiry, the small boats crisis, the Chagos islands deal which have left Sir Keir's premiership in tatters.
"Whether it's on welfare, grooming gangs, small boats, all of the promises that Labour made are broken, and we've still got four more years of this - this is just the first year," she said.
Despite the embarrassing reversals, Sir Keir boasted of his "real sense of pride and achievement" at marking his first year in power.
No 10 pointed to the three trade deals struck with India, the US, and the EU, the extra investment in the spending review, and a cut in NHS waiting lists among the Government's achievements one year on.
The PM's spokesman added: "He said the Government's work is all designed and focused on improving the lives of working people and giving them the chance to thrive, not just survive, and the Government should be proud of those achievements as a team."
Sir Keir's upbeat tone came despite being engulfed in crisis on multiple fronts.
Channel migrants have already hit 20,000 this year, the earliest the tally has been reached.
Meanwhile, there are mounting fears that Rachel Reeves will have to hike taxes again this Autumn as the economy stalls and angry MPs force U-turns wrecking her plans to balance the books.
Polls have shown the government's popularity nosediving since securing one of the biggest majorities in modern UK politics.
Nigel Farage's Reform are now enjoying a clear advantage in support, with panic rising in Labour circles about Sir Keir's leadership.
London and Manchester Mayors Sadiq Khan and Andy Burnham are said to be on manoeuvres, while Angela Rayner's allies are also talking up her credentials.
The premier caused more dismay at the weekend by backtracking on his "island of strangers" remark about the dangers of uncontrolled immigration.
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