Tony Blair today pledged to cut hospital waiting times to a maximum of 18 weeks before he steps down.

The move came as the government's NHS reforms came under renewed attack from doctors and health unions.

But accompanied by the health secretary, Patricia Hewitt, on a tour of King's College Hospital in south-east London, Mr Blair stressed that the NHS had to carry on changing in order to cut patients' waiting times.

"Of course there are always ways you can make the changes better, but if you imagine getting to this 18-week maximum - that is for the whole process from the time you see your GP and are diagnosed right through to the operation - that will be a real transformation within the health service," Mr Blair said.

"But it will only be done if we carry on the process of change... Just like everything else in the 21st century, the NHS cannot carry on as if the world was still as it was decades ago."

The deadline for hospitals to hit the 18-week target is not until the end of 2008, well after Mr Blair is expected to stand down as prime minister.

Asked how much of the process he wanted to oversee, he said: "The most important thing is to put in place that framework that will deliver this 18-week target.

"If we can do that by the process of change, however difficult it is and however understandable the resistance is to it, that will in 10 years transform what was the biggest problem in the national health service: the fact that people had to wait months and months, often in pain and sometimes even dying, for want of their operations.

Ministers hope the new target will steer the health agenda away from record NHS deficits.

But a survey of more than 3,000 doctors found that most do not believe the health service is safe in the government's hands, while the UK's largest union, Unison, warned that using private companies to do NHS work was exacerbating financial problems.

Mr Blair said that the introduction of 24-hour surgery would help to meet the 18-week target.

A nationwide campaign is to be launched next month "to focus the activities of all NHS staff" on cutting waiting times, with hospitals encouraged to consider sending more patients abroad and increasing the use of the private sector.

But Dr Jonathan Fielden, deputy chairman of the British Medical Association's consultant committee, warned that meeting the target could come at the detriment of other areas of NHS care, such as care for long-term conditions and mental health.

Dr Fielden told BBC Radio 4's Today programme: "If you just focus on production lines and churning people through, we won't look at the broader picture and we need to do that."

A survey of 3,092 doctors, published today, also questioned the effectiveness of the government's healthcare reforms. The online poll found that nearly three-quarters (72%) do not believe the extra billions invested in the NHS have been well spent.

More than half (56%) of the respondents said there had been no improvements since 2002, when the government increased funding, while only 27% thought there had been.

The survey found that doctors were disillusioned with central government control, angered by the growth of bureaucracy and deeply sceptical of initiatives such as the £20bn NHS IT system

Most doctors said they believed Labour had failed to reform the NHS and nearly twice as many would trust the NHS with the Tory leader, David Cameron, than with the chancellor, Gordon Brown. However, a larger number said they would trust neither.

The poll, conducted by medical website doctors.net for the Times, also found that doctors believe there will need to be a radical rethink of NHS funding after 2008, when current annual funding increases are expected to drop off.

Nearly four-fifths (79%) of respondents said high standards could not be sustained through taxation alone.

In a separate report, Unison said that private firms contracted to do NHS work were making "obscene" profits and opening up a "black hole" in the health service's finances.

The report said increasing privatisation of the NHS was leading to redundancies and problems finding jobs for newly qualified nurses, midwives and physiotherapists.

But Ivan Lewis, the junior health minister, said the Unison report was "misleading and factually inaccurate".

He said: "If private organisations can help the NHS deliver better services for patients and better value for taxpayers, we will use them. If they can't, we won't."