Labour has warned that the NHS is "heading for the rocks" as it called for contracts putting the service "up for sale" in England to be frozen until after the general election.
Andy Burnham accused the Government of creating a part-privatised, two-tier health market and suggested that five more years of the same would " push the NHS off the cliff-edge".
Decisions made after the next general election will determine the future of the service, or even whether it has one, the shadow health secretary warned.
In a speech in Manchester, he claimed that the Government's reorganisation of the NHS has led to a sustained fall in standards, an accelerated postcode lottery and privatisation.
"The NHS has arrived at a major crossroads," he said. "The 21st century is asking some difficult questions of our 20th century service and, in truth, it is struggling to answer them.
"Such is the scale of the challenges looming over the NHS in the next Parliament that the decisions taken will determine its future - or indeed whether it has one."
Mr Burnham c laimed the Prime Minister was "not up front" about his intentions for reform during the 2010 campaign, leaving voters with no say.
He said forced privatisation is being pushed through "at pace and scale" and warned that contracts being signed now will bind the next government.
Since the Health and Social Care Act was introduced, the bidding for two contracts for cancer care in Staffordshire worth a total of £1.2 billion and lasting for 10 years has been opened up to the private sector along with a five-year contract worth £800 million for the care of older people in Cambridge.
Mr Burnham has written to NHS England boss Simon Stevens calling for a halt to any further contracts for NHS clinical services being signed until after the next election except where there are issues of patient safety or urgent threats to service provision.
" It all amounts to the mismanagement of the country's most valued asset on a grand scale," he said.
" The NHS can't carry on like this. It is heading for the rocks and we urgently need a plan to turn things around."
He added: "Contracts are being signed that will run for the five years of the next Parliament, and beyond. This is not acceptable. Contracts like this will tie the hands of the next government in a crucial area of public policy.
"But, even worse, they are being signed without a mandate from the public. The Prime Minister was not up front about these plans at the last election. He needs to be reminded that he has never been given the permission of the public to put the NHS up for sale in this way."
The Conservatives accused Labour of posturing. A spokesman said: "This speech is all about politics - it's not a serious plan for the future of the NHS.
"Use of the private sector by the NHS doubled in the last four years of Labour, a far bigger increase than under this Government. Andy Burnham himself signed off the privatisation of Hinchingbrooke Hospital during Labour's final year so it is pure political posturing to try to interfere with doctors making the best clinical judgments for patients.
"The most important thing with NHS care is that it is high quality and free at the point of delivery. Because of the realistic assessments this Government has made on public spending, we've been able to do exactly that. We've increased health spending, increased the number of doctors and reduced the number of managers.
"The NHS is an asset to be valued and protected - it deserves better than this speech. The real choice at the next election will be between a Conservative Party which is delivering a more efficient and effective NHS - and a Labour Party which has learned nothing from its past mistakes."
Unite general secretary Len McCluskey said the Health and Social Care Act had been a disaster for the NHS.
He added: "David Cameron is behaving like an estate agent who has put a big for sale sign up outside your home without permission. The Government's odious health act is being used to sell-off huge swathes of NHS clinical services from cancer care to in-house pharmacies. Since the Government's health act came in to force, 70% of health services put out to tender have gone to the private sector."
Labour accused ministers of making "dodgy claims" about the state of the NHS, after the national statistics watchdog said that Health Secretary Jeremy Hunt ought to consider correcting an assertion he made in the House of Commons about declining waiting times.
UK Statistics Authority chairman Sir Andrew Dilnot also indicated that Mr Cameron's high-profile claim in the Commons that average waiting times in NHS A&E departments in England were "down by more than half" under the coalition did not reflect the "most complete" set of statistics available.
Mr Cameron's claim has already been questioned in a paper published by the House of Commons Library, which argued that the PM was relying on a "simplistic reading" of statistics and that the data "did not support" his assertion that casualty waits had fallen from 77 minutes under Labour to just 30 minutes. But the paper was swiftly removed from the Library website on the grounds it did not meet impartiality requirements.
Now, Sir Andrew has analysed Mr Cameron's claim and found that it reflected only the measure of how long patients had to wait to be assessed in A&E. While the mean average waiting time for assessment had indeed tumbled from 77 to 30 minutes between 2009 and 2013, the median average remained virtually static at around 8-9 minutes.
When preparing information for parliamentary answers, the Health and Social Care Information Centre (HSCIC) would normally focus on the length of time patients wait to leave A&E, as these figures are "likely to be the most complete", he said. These "duration to departure" waits rose on a mean average from 135 minutes in 2009-10 to 141 in 2012-13 and a median average of 122 minutes to 128 minutes over the same period.
Sir Andrew also said that Mr Hunt had muddled the figures for mean and median waits for assessment in comments to the Commons in June and said that he "may wish to take advice on whether it is necessary to correct the parliamentary record".
Mr Burnham said: "Not for the first time, David Cameron and Jeremy Hunt have been found out making dodgy claims about the NHS from the Despatch Box. It proves their statements on the NHS, even in the House of Commons, can no longer be trusted.
"Sir Andrew Dilnot confirms that waiting times in A&E have got worse on this Government's watch. But his analysis concludes that things are even worse than we thought, with hospital A&Es missing the Government's lowered target in every quarter for almost two years.
"This is a damning verdict on David Cameron's and Jeremy Hunt's mismanagement of the NHS and their desperate attempts to paper over the cracks. The gap between their spin and the reality for patients is becoming dangerous. Cameron and Hunt need to start putting patients before their own PR and produce a plan to halt the decline in A&E."