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Sir John Major has branded the Tories' flagship welfare reform “operationally messy, socially unfair and unforgiving”.

The Tory ex-PM waded into the furore over the roll-out of Universal Credit, which combines six working age benefits into a single payment.

More than a dozen Tory MPs have urged ministers to pause the roll-out of the policy amid concerns that claimants could face delays in receiving money.

And Dame Louise Casey, the ex-head of the government's troubled families team, warned it was like "jumping over a cliff" for people with no spare money.

Government figures show 23% of new claimants do not receive their first full payment within six weeks, which has been linked to rent arrears and other debts for claimants.

Calling for a review, Sir John wrote in the Mail on Sunday that though the overhaul is “theoretically impeccable”, it is “operationally messy, socially unfair and unforgiving.

It is time for the Conservative Party to show its heart again, which is all too often concealed by its financial prudence. We are not living in normal times and must challenge innate Conservative caution”.

A report reveals that among Universal Credit claimants who pay rent, 41% are in arrears, with 82% saying it is for the first time.

(Image: Getty)

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The study, carried out for the Department for Work and Pensions and revealed by the Sunday People, also shows large numbers are forced to borrow, with 7% turning to doorstep lenders and 5% taking payday loans.

Almost 30% rely on a loan from family and friends.

Calling for further action on housing and education, Sir John urged Chancellor Philip Hammond to ease up on austerity.

Sir John suggested that the Government could take advantage of low borrowing costs to fund investment in the country's future.

"We must persuade the Treasury that - while the cost of long-term borrowing is low - there is an opportunity to vastly accelerate public development of infrastructure and, in particular, housing.

"Useful initiatives have been announced but we need to go further. if this increases public debt we should - and could - accept that (as I believe the markets will) provided annual revenue expenditure is kept under control."

Sir John was scathing about those agitating for a change in Tory leadership behind the scenes.

He said he was "saddened to see the news dominated by those who have been driven by their own personal agenda" adding "their conduct has undermined their own party, their own Prime Minister, and their own Government".

The comments will be viewed as a slapdown to Foreign Secretary Boris Johnson, whose activities overshadowed much of the Tory conference until Mrs May's ill-fated speech.

"The country has had enough of the self-absorbed and, frankly, disloyal behaviour we have witnessed over recent weeks," Sir John said.

"It is time for the individuals concerned - both in Parliament and in Government - to focus their minds instead on the needs of the British people, rather than on their own personal ambition."