Cabinet ministers are writing to the prime minister in an urgent attempt to soften some of the spending cuts being demanded ahead of the budget.
The main measures for the budget have to be decided by the end of Wednesday and sent to the Office for Budget Responsibility before the Treasury shuts up for the evening.
Sky News can confirm letters from cabinet ministers complaining about the budget have gone over the head of Chancellor Rachel Reeves to Sir Keir Starmer and Number 10.
Politics latest: Cabinet members deeply concerned over scale of cuts
Some of these letters are believed to have gone in over the last couple of days.
After today, only small changes can ordinarily be made to the budget, typically around involving items of tens or hundreds of millions rather than billions.
Some cabinet ministers are deeply concerned about the scale of the cuts being demanded in some areas to fund pay rises and spending increases elsewhere. The existence of the letters was first reported by Bloomberg.
At the weekend, Sky News revealed one cabinet minister saying: “The briefing doesn’t match the reality. It’s pain this year, and pain next year. We’re simply going to be digging a hole which we end up filling in later in the year.”
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Ms Reeves will loosen the borrowing rules in the budget in order to give herself more room for spending, along with raising up to £40bn in tax rises and welfare cuts in order to relieve pressure on budgets.
But the cost of significant public sector pay rises, which are still going to have to be found from within departmental budgets, mean cuts this year and next are still being demanded by the Treasury.
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Some ministers believe the cuts are unsustainable, while some have pointed to the first round of spending reductions announced before the summer – including the winter fuel allowance changes – as evidence more input from Number 10 is needed ahead of the budget and spending review on 30 October.
One government source told Sky News: “The whole of Number 10 is focused on the budget at the moment and there isn’t much bandwidth for anything else.”
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Government figures insist that letters voicing concern are routinely sent at this point in a spending review process and that this is all normal.
Both Sir Keir and Ms Reeves are out of the country next week, the week before the budget. However, only smaller changes can typically be made after today to the shape of it.