Confidence among GPs that the Government's NHS reforms will improve patient care has almost halved since they were first proposed, an opinion poll shows.
Only around one in eight (12%) now expects health service users to be better off as a result compared with nearly a quarter (23%) two months after the blueprint was published in July 2010.
More than half (55%) said care would not improve with 33% not expressing an opinion either way in the survey by ComRes by the BBC.
Legislation putting the shake-up into effect finally became law last week after a turbulent passage through parliament that saw it significantly rewritten amid hostility from many health professionals.
But ministers are braced for a continued battle as the measures - which include putting control of up to £80 billion of commissioning into the hands of local consortia of GPs from April 2013 - are put into effect.
Labour have pledged to continue their opposition to reforms, encouraging health professionals to resist what they see as creeping market forces within the NHS.
And some doctors have threatened to unseat coalition MPs at the next election.
The poll of 814 GPs showed 83% also feared financial pressures will lead to more rationing of care.
Dr Laurence Buckman, chairman of the British Medical Association's GPs committee, told the BBC the results were in line with what his organisation was hearing from doctors.
"If those who will have to deliver the latest health reforms are unconvinced and reluctant, the Government should take notice of what they say," he said.
Shadow health secretary Andy Burnham said: "It is clear David Cameron convinced nobody with his rhetoric and had to resort to ramming his Bill through Parliament.
"Any hopes he had that the concerns of NHS professionals would now subside are blown out of the water by this. Instead, GPs are clearly worried about the future of the NHS, warning of longer waits, service rationing and creeping privatisation.
"Many will lay responsibility for these things directly at the Prime Minister's door."
Health Secretary Andrew Lansley said: "The Health and Social Care Act will hand power to GPs, put patients at the heart of the NHS, and reduce needless bureaucracy.
"Of course, every important reform to the NHS, under whatever government, has had its critics from within the system.
But putting GPs in leadership positions in the NHS will mean they can improve services for their entire local population. Patients want doctors to make decisions about their care, not managers, and that is what our reforms will deliver.
"The independent NHS Future Forum found broad support for the principles of our plans. And we have seen GPs themselves, as well as across the service, outline support for shifting power to the front line.
"We know the NHS can be more efficient - it has already made £7 billion in efficiency savings since April 2010 whilst improving performance - there are record low infection rates, mixed sex wards down by over 90 percent and the number of people waiting over a year for treatment has been reduced by over half."