Chancellor Philip Hammond is facing calls for an urgent cash injection to head off a looming "crisis" in social care when he delivers his first Autumn Statement next month.
Sarah Wollaston, the Conservative chairwoman of the Commons Health Committee, has written to Mr Hammond warning the adult social care sector was approaching a "tipping point" - with potentially serious implications across the NHS.
In a strongly worded letter, she upbraided ministers for giving the "false impression" that the NHS in England was "awash with cash" at a time when the pressures on its finances were threatening to become "overwhelming".
She also warned the Chancellor that unless the Government was able to put capital investment in the NHS on a sustainable footing, the service would struggle to meet the long-term demands of caring for an ageing population.
Her warning was echoed by NHS Providers which said there was now a "big risk" that trusts would be unable to maintain current levels of service.
In her letter, signed by four other committee members including the Conservative Dr James Davies, Dr Wollaston took issue with the Government's claim that it was raising spending on the NHS in England by £10 billion over the next five years.
"The continued use of the figure of £10 billion for the additional health spending up to 2020-21 is not only incorrect but risks giving a false impression that the NHS is awash with cash," she wrote.
"This figure is often combined with a claim that the Government 'has given the NHS what it asked for'. Again, this claim does not stand up to scrutiny as NHS England spending cannot be seen in isolation for other key areas of health spending."
A Government spokesman insisted the £10 billion figure was accurate and that it was "wrong to suggest otherwise".
However Dr Wollaston said a substantial part of the increase came from cuts of £3.5 billion to health spending which fell outside the NHS budget such as the public health grant to local authorities and education and training paid for by Health Education England.
Overall, the increase to total health spending in England - the Department of Health's budget - was £6 billion over the period 2014-15 to 2020-21 - or £4.5 billion over the current spending review period of 2015-16 to 2020-21.
While Dr Wollaston acknowledged the settlement appeared "generous" compared to other departments, she said the inflationary pressures on the NHS from a growing and ageing population were "far greater".
She flatly rejected suggestions the NHS could learn from the example of the cuts which Mr Hammond and Theresa May were able to drive through when they were at the Ministry of Defence and the Home Office.
"Despite the real-terms increases set out in the spending review, per capita funding for the NHS is projected to be flat in 2017-18, and actually to fall in 2018-19," she wrote. "That calls into question the ability of the NHS to maintain services in the latter part of the spending review period."
However, she said the most immediate problem was with adult social care, where the entire funding precept raised by local authorities through the council tax had been swallowed up meeting the demands of the living wage.
With the Care Quality Commission warning the sector was approaching a "tipping point", she said that unless there was urgent action the knock-on effects of increased A&E attendances and longer hospitals stays could undermine the whole NHS five-year plan.
"Numerous sources testify to the impact of the real terms cuts to social care, not only to the vulnerable people who rely on care, but also on NHS services," she wrote.
"There is an emerging consensus across the NHS that any additional money which might be available in the Autumn Statement should be directed first towards social care. We agree."
NHS Providers chief executive Chris Hopson welcomed Dr Wollaston's "clear-sighted analysis", saying: "The gap between what the NHS is being asked to deliver and the funding it has available is too big and is growing rapidly."
A Government spokesman said: "The Government has backed the NHS's own plan for the future with a £10 billion real-terms increase in its funding a year by 2020/2021, helping to ease the pressures on hospitals, GPs and mental health services.
"We have also allowed local government to increase social care spending by the end of Parliament, with access to up to £3.5 billion of new support."