Health experts have issued a stark warning that the NHS is "not ready" on the day that massive changes in the organisation 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 that 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.
When asked whether the NHS is ready for such a big change, 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.
"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."
Labour said that the reforms have exposed the health service to risk because they have been implemented during a time of huge financial pressure.
The main aim of the health reforms was to make the NHS more accountable to patients and to release frontline staff from excessive bureaucracy and top-down control.
One of the biggest changes is the move from primary care trusts (PCTs) to clinical commissioning groups (CCGs), which will be led by GPs and other clinicians who will take on responsibility for commissioning care. The move will see 211 CCGs replace 151 PCTs across England.
But last week it was announced that only half of of the new CCGs will be fully ready to start work when the changes come into effect on April 1. Just 106 CCGs are "fully authorised", said NHS England.
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".
A spokesman said that under the new system patients will be given more choice in who provides their care and a stronger voice through a new consumer champion Healthwatch England and the "friends and family test".
Health Minister Lord Howe said: "The NHS needs to change so that patients get the care they need, when they need it."
He added: "Health and care services will be better joined up by bringing together the NHS, local councils and patients.
"Patients will have a greater influence in changes to their local health and care services through the patient led inspections and the friends and family test."