The proposed reforms to the NHS will harm progress and increase bureaucracy, a representative of the British Medical Association has claimed.
After meeting health professionals at Downing Street, David Cameron reasserted his "commitment" to the reforms which he believed would improve the NHS.
BMA chairman Hamish Meldrum, who was not invited to the meeting, said that the bill, designed to pass the responsibility for health commissioning to GP consortia from primary care trusts, would have the opposite effect.
"Doctors and other clinicians are always looking for the opportunity to find better ways of helping patients get the care they need - if possible, closer to home," he said.
"It is encouraging that emergency hospital admissions fell last year but one of our biggest concerns about the bill is that the increasing bureaucracy and focus on competition it brings will get in the way of this sort of progress.
"Clinical commissioning is a good concept and is already demonstrating success without the need for legislation. So we have to ask why put this at risk, especially at this time of huge financial pressure?"
Health secretary Andrew Lansley saw the strength of feeling against the bill when he came face to face with outspoken protesters outside Downing Street.
The bill has come under fire from across the health service. A YouGov poll carried out for the union Unite shows the public trusts medical professionals more than politicians on health.
"It is extremely disappointing that the government seems increasingly to be indulging in selective listening," said Meldrum.
"The BMA represents nearly 150,000 doctors - in hospitals, community services and general practice. We want to find a way to make sure patient care continues to improve.
"If the government shares this objective, it has to recognise that NHS reform must have the support of these, and all other, health professionals."