Tony Blair has insisted now is the time to "hold our nerves" over NHS reforms in the face of criticism.
Many staff fear for their jobs
The prime minister told a group of doctors and nurses the NHS had reached the "crunch point" in its 10-year reform programme.
Structural change within the NHS to give patients greater choice will be the next focus of reform, he said.
His speech comes amid concern over financial deficits in NHS trusts and the announcement of 7,000 job cuts.
Mr Blair said he wanted to create an NHS for "2008, not 1948".
In a speech to the New Health Network think tank, he said he would not shy away from "tough decisions" to be made over the health service.
He admitted there would be a year of challenge "as the new system bites".
But Mr Blair said: "This is not the moment to back away or dilute these changes, but rather the moment to hold our nerve, back the change-makers in the NHS who are making it happen, and see the process of change through.
"Each reform was in its time opposed, each reform is now considered the norm and the lesson especially at this point of difficulty is if it's right do it - in fact do more of it.
"Take the tough decisions which are not the cause of the NHS problems but the route to making the NHS even better,even fitter for the modern world."
The prime minister said record investment had been made in the health service - and services had improved as a result.
"We have to hold our nerve, see it through, do what is necessary, so that the NHS in the years to come is not just a great institution for which people feel enormous sentimental and emotional attachment, but is delivering the high standard and quality of care that people in the early 21st century expect from any public service."
Only last week the prime minister met local NHS bosses where he vowed to push on with NHS reforms.
Under the proposed changes Strategic Health Authorities and Primary Care Trusts will be streamlined to help them focus on the commissioning care.
The NHS is also moving to a system of "payment by results" designed to ensure money follows the patient.
Shadow health secretary Andrew Lansley said no amount of rhetoric would "cover up the government's gross mismanagement of NHS finances".
"In reality, we've had more spending, more bureaucracy, more waste and higher costs but without necessary reform nor rising productivity," he said.
Steve Webb, for the Liberal Democrats, said: "The prime minister's desperate desire to secure a 'legacy' before he stands down has resulted in a swathe of reforms all being rushed through at once, creating turmoil in the NHS."
While NHS Trusts have recently announced 7,000 job cuts, a report by the centre-right think-tank Reform has predicted up to 100,000 could go, as many trusts face budget deficits.
The Daily Telegraph suggests that dozens of hospitals could be shut down or forced to make cuts in services as managers respond to changes in the way NHS trusts are funded.
Karen Jennings, head of health for Unison, said: "Blair may say we need to hold our nerve over NHS reforms - I say that he has a nerve to sit back and oversee hospitals closing, swingeing job cuts and privatisation."