Theresa May needs to "seriously reconsider" the NHS budget because the Government's current plan is unsustainable, a spending watchdog has said.
Public Accounts Committee chairwoman Meg Hillier said she was "dismayed" about the Government's response to recent warnings from the Health Select Committee chairwoman that per capita spending in the health service is set to fall in 2018/19.
Sarah Wollaston warned ministers they were giving a "false impression" that the NHS was being boosted by £10 billion over the five years of its spending review, when the real figure was £4.5 billion.
But a Government spokesman insisted the £10 billion figure was accurate and that it was "wrong to suggest otherwise".
In a letter to the Prime Minister, Ms Hillier said her "concerns about the sustainability of the budget were very clear".
She wrote: "I was dismayed that the official Government response was to deny there was any issue. This flies in the face of the evidence that our committees and the National Audit Office has uncovered.
"The mantra from ministers and officials is that transformation and efficiencies are achievable at a scale that will solve the problem. In reality there are a number of pressures which even the most ambitious and successful transformation programme would be hard pressed to deliver.
"Growing patient demand is at the base of the funding crisis. Monitor, NHS England and independent analysts have previously calculated that a combination of growing demand, if met by no further annual efficiencies and flat real terms funding, would produce a mismatch between resources and patient needs of nearly £30 billion a year by 2020/21."
Ms Hillier also accused Mrs May of ignoring the evidence of whistleblowers who have raised concerns about budgetary pressures.
She said: "The fact that the budget pressures were predictable, but that few senior NHS figures were willing to say so publicly, underlines a key issue for ministers.
"Too often NHS personnel raising concerns find themselves pariahs in the system.
"There is a long list of formal whistleblowers who have never worked in the NHS again as a result of their willingness to raise their concerns.
"I fear that this lack of willingness to talk truth to those in charge extends right up to No 10.