Chancellor Rachel Reeves faces a £9billion black hole in the NHS budget left by the Tories, according to an analysis seen by the Treasury.
Government insiders have warned that without extra funding at the Budget the gap would see millions of appointments, scans and operations cancelled.
They also claim it would lead to 21,000 senior doctors and 81,000 nurses losing their jobs while waiting lists would soar past record levels without emergency cash.
A Treasury source said: “The Conservatives' crashed the economy and then they ran away - leaving the NHS with spending plans that were total fiscal fiction. They would take the NHS beyond breaking point and kill the service for good." They added: "Once again, it falls to a Labour government to clean up the Tories' mess and fix the NHS”.
Be the first with news from Mirror Politics
WHATSAPP GROUP: Be first to get the biggest bombshells and breaking news by joining our Politics WhatsApp group here. We also treat our community members to special offers, promotions, and adverts from us and our partners. If you don’t like our community, you can check out any time you like. If you’re curious, you can read our Privacy Notice.
NEWSLETTER: Or sign up here to the Mirror's Politics newsletter for all the best exclusives and opinions straight to your inbox.
PODCAST: And listen to our exciting new political podcast The Division Bell, hosted by Mirror interim political editor Lizzy Buchan and Express political editor Sam Lister, every Thursday.
They highlighted figures from the Health Foundation in June that warned the NHS needed funding to grow by an average 2.9% a year just to stand still. The charity said at the time: "Around two-thirds of the increase would be needed just to keep pace with population growth and the rising number of people living with major illness."
Just after the General Election, Ms Reeves also accepted recommendations from the independent pay review bodies for millions of NHS staff. The government has accused the defeated Tories of failing to budget for the pay hikes - accounting for around £4billion in the total black hole.
The alert comes after The Mirror first reported last month the Chancellor will put hospitals and cutting waiting lists at the heart of Labour's first Budget in 15 years.
But there are jitters at the top of government over possible tax and spending plans - despite Keir Starmer's promise there will be no return to austerity. In recent days some Cabinet ministers have even written to the PM expressing concern over proposals for their own Whitehall budgets.
Downing Street warned that "not every department will be able to do everything they want to" and "tough decisions" would have to be made.
It came as Ms Reeves told her colleagues at a Cabinet meeting this week she will stand by her commitment to "fix the NHS", But she also warned them that the dire inheritance left by the Tories meant there would be "difficult decisions on spending, welfare, and tax".