Health experts have warned that NHS is "not ready" for the raft of changes implemented under the controversial health reforms - which have now come into effect.
The Health and Social Care Act, which became law after a tortuous passage through Parliament, is expected to cost the taxpayer between £1.5 billion and £1.6 billion to implement.
Nick Black, professor of health service research at the London School of Hygiene and Tropical Medicine, said he did not believe the health service was prepared for such a huge structural change.
He warned that hospitals could "grind to a halt" as cuts to social care budgets mean that doctors are unable to discharge patients who do not need to be on the wards. And Labour said that the reforms have exposed the health service to risk because they have been implemented during a time of huge financial pressure.
When asked whether the NHS is ready for such a big change, Prof Black said: "Not really no. It could really do without this. What we have got at the moment is a perfect storm with three major things happening - the changes in the structure, the fall out from Francis and the Nicholson challenge (where the NHS has been tasked with making £20 billion in efficiency savings during the four years to 2015)."
"At one level patients won't notice anything dramatic on Monday morning. But the biggest thing that patients will notice will be the knock-on effect from the cuts in social care funding. It is clear that our hospitals are already struggling to discharge patients. One manager who I spoke to last week said that 100 beds in his hospitals could be discharged if there was the care in the community. Hospitals could cease to function and the system could grind to a halt because of people who do not need to be there."
Rachael Maskell, head of health at union Unite, added: "There is every indication that the NHS is not ready for the changes. The time scale was totally unrealistic."
The Civitas think-tank said the reforms were a "distraction" from the need for more radical NHS, including opening it to more competition. It commissioned an ICM poll which found 83% of voters were not concerned who delivered health services so long as they remained free at the point of delivery.
Director David Green said: "The reforms taking effect from today are a distraction that will not empower consumers or encourage diverse ownership to the extent required. The best way to raise standards and look after patient interests is to promote competition so that rival providers are compelled to raise their game. We all know as consumers that, unless we have alternatives, producer interests come to dominate."
The Department of Health said that for the first time health and social care services will be "designed around the needs of the local community".