Ministers are asking the Prime Minister to urgently try to ease some of the spending cuts requested before the budget is adopted.
Major budget measures must be decided by the end of Wednesday and sent to the Office of Budget Responsibility before Treasury closes its deliberations in the evening.
Sky News can confirm that letters from ministers complaining about the Budget have gone from Chancellor Rachel Reeves to Sir Keir Starmer and No 10.
Latest policy news: Cabinet members are deeply concerned about the scale of the cuts
Some of these letters are believed to have been received in the last few days.
As of today, only small changes can usually be made to the budget, usually affecting items in the tens or hundreds of millions rather than billions.
Some ministers are deeply concerned about the scale of cuts demanded in some areas to fund pay rises and increase spending in others. The existence of the letters was first reported by Bloomberg.
Over the weekend, Sky News revealed that one minister said: “The briefing does not reflect reality. There will be pain this year and next year. We will just keep digging a hole that will eventually be filled later in the year.”
Mrs Reeves will loosen the borrowing rules in the budget to give herself more room for spending, with tax increases worth up to £40 billion and cuts to social benefits to ease pressure on budgets.
However, the costs of significant public sector pay rises, which will still need to be found in departmental budgets, mean that the treasury continues to demand cuts this year and next.
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Some ministers believe the cuts are unsustainable, while others pointed to the first round of spending cuts announced before the summer – including changes to the winter fuel allowance – as evidence that more input from No 10 is needed ahead of the budget and spending review on October 30.
One government source told Sky News: “The entire focus of No. 10 is on the budget at the moment and there is not much room for anything else.”
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Government figures insist that letters of concern are routinely sent at this stage of the spending review process and that this is normal.
Both Sir Keir and Mrs Reeves leave the country next week, a week before the Budget. However, after today, you can usually only make minor changes to its shape.
