David Cameron warned today that the NHS will become "increasingly unaffordable" if radical plans by the Government to reform the NHS are not implemented.
The Prime Minister defended an overhaul of the NHS, including handing GPs £80 billion of the NHS budget to commission services, insisting that the "biggest risk" to the NHS would be to do nothing.
"If you look at the growth of the elderly population, look at the new drugs that are coming on stream, the new treatments, if we keep the system we have now and don't make changes to cut bureaucracy and waste, I think it will become increasingly unaffordable," he told BBC Breakfast.
"The risk is doing nothing."
Mr Cameron's remarks came as protesters opposed to the reforms planned to demonstrate outside Parliament as ministers begin a second debate on the controversial Health and Social Care Bill.
Mr Cameron defended the plans against criticism from health service unions and rejected claims that the reforms amounted to privatisation.
"Of course, some of the trade unions are nervous about this because it will mean greater choices for GPs and patients, it will mean that, for instance, they will be able to choose between hospitals and between services and sometimes trade unions don't like that sort of choice," he said.
He said he wanted to reassure the public that no privatisation was taking place.
"There is no privatisation taking place, the NHS will be just like you experience it now - it is free at the point of use, you don't pay anything, and it is according to your need," he said.
"But I think it is a good thing if patients and their GPs are able to choose between different providers."
Mr Cameron's defence of the plans comes as Unite, the country's biggest union, is expected to present MPs with "new and forensic analysis" of the legislation before the second reading, amid claims that the coalition is "rushing through" the 280-clause Bill.
A recent survey revealed that only one in four people supports doctors using private companies to provide NHS services.
The survey of almost 2,000 adults for public sector union Unison showed that half were opposed to the move, including 56% of Liberal Democrat voters.
Only 46% of Conservative voters supported private firms providing NHS services, with 22% registering a "don't know" response.
The YouGov study also showed that half of those surveyed were against GPs employing private management groups.
Unison general secretary Dave Prentis said: "This Bill is heading for trouble. The YouGov poll shows a clear split between Lib Dem and Tory supporters. There is very weak support from Tory voters and clear opposition from Lib Dems.
"The fact is there is very little support for this Bill from anywhere. Many GPs are opposed to it, as are patients, NHS staff, clinicians, charities, think tanks, MPs and unions. The Government's vanity project is undemocratic, unaffordable and unnecessary.
"The NHS is already under severe financial pressure because of Government demands to make £20 billion in so-called efficiency savings.
"This titanic reorganisation threatens to sink the NHS. The Government should step back from the brink and pronounce this Bill DOA - dead on arrival."
Health workers from up and down the country will congregate outside Parliament today, carrying estate agent signs bearing the message "NHS, Not for Sale".
Unite said it understood that the Bill could begin its Standing Committee stages as early as Thursday of this week, leaving little time for MPs to get to grips with the "enormity" of the proposals.
It said the Bill will hasten the privatisation of the NHS, claiming that the legislation is heavily weighted in favour of private companies when they come into competition with the current NHS.
The union has repeatedly warned that the Government's proposals will speed up the "demise" of the NHS's universal service, free at the point of delivery and cherished by the public since its founding in 1948.
Gail Gartmail, assistant general secretary of Unite, will tell MPs today: "This Bill will destroy the NHS. It will allow NHS staff, skills, buildings and resources to be snatched by profit-hungry companies. It will shove NHS patients to the back of the queue as private greed will leapfrog health need every time.
"It will open up huge ravines of inequality in our communities as GP businesses close their doors to those with costly care needs.
"It will encourage the sort of bloated rewards for the health privateers we see at the top end of banking; do we really want the values which have shamed the City tainting our health service?
"The checks and balances in this colossal Bill are few and far too flimsy for change of this magnitude. Our Government is abandoning a 60-year role as the provider and protector of quality healthcare for all. It is fully intending to force the NHS to swim with the private sector sharks while it rows off speedily in the other direction.
"All this will be done without a shred of evidence to prove that it will improve the health of a single patient.
"Nobody wants this Bill - not the professionals or the patients. This is shameless state-bashing by the Government. It is a shocking misuse of their power, it will cause misery for needy people and it must be stopped."