Doctors have dismissed the coalition's changes to its health plans as inadequate to protect the NHS and demanded that the controversial health and social care bill be withdrawn altogether.

Delegates at the British Medical Association's annual conference defied calls from the union's leadership and backed a motion that demanded further big changes to key elements of the bill.

Large majorities of the 500 delegates at the BMA's annual conference in Cardiff voted for a motion, underlining the fact that many medics remain fearful for the NHS's future, despite the recent concessions over the bill.

Doctors' representatives expressed serious unease that changes to the bill agreed by ministers after the NHS Future Forum report do not go far enough.

The government was also accused by Labour today of retaining key elements of the controversial reforms, despite promising to change them in the wake of its NHS "listening exercise".

The shadow health secretary, John Healey, said that despite ministers tabling 180 amendments to the bill, the Tories' long-term aim of breaking up the NHS and establishing a "full-scale market" remained intact.

The BMA conference passed a motion that said the government's response to the forum's report earlier this month "fails to satisfactorily address the concerns of the profession". It identified four key areas of continuing anxiety about the reformulated bill, which has begun a second period of scrutiny in the House of Commons by a public bill committee of MPs.

Speakers argued that the Secretary of State for Health's duty to provide comprehensive health services in England – which ministers said they would restore after it was removed in Andrew Lansley's original version of the bill – was still not guaranteed. They rejected the reassurance of the BMA's leader, Dr Hamish Meldrum, that legal advice taken by the union meant that the minister would remain ultimately responsible in the future.

Delegates also voiced dissatisfaction that the health regulator, Monitor, would still promote competition between hospitals as envisaged by Lansley in his NHS blueprint, which led to a split in the coalition, despite David Cameron agreeing to replace it with a duty to promote integration of services instead. They voted by 70% to 22% to defy Meldrum's advice that the duty to promote competition "has gone" as part of the government's rethink.

Delegates also backed, by 93% to 5%, the part of the motion that argued "that competition should not be forced on the NHS by imposing any duties on commissioners to promote choice as a higher priority than tackling fair access and health inequalities".

Meldrum warned that a vote to withdraw the bill altogether would weaken the BMA's position in ongoing negotiations with the government. Delegates nevertheless voted by 59% to 35% for the union to continue to call for the bill to be withdrawn rather than simply amended.

The vote is a setback for Meldrum, but will make little difference to the passage of the bill through the Commons, especially as Liberal Democrat MPs' fears about it have now been successfully neutralised.

A Department of Health spokesman said: "This vote is disappointing, because only a few weeks ago the doctors' union said there was much in our response to the listening exercise that addressed their concerns, and that many of the principles outlined reflected changes they had called for.

"The independent NHS Future Forum confirmed there is widespread support for the principles of our plans to modernise the NHS, including handing more control to doctors, nurses and frontline professionals.

"The bill has changed substantially since the BMA first voted to oppose government policy. Our plans have been greatly strengthened in order to improve care for patients and safeguard the future of the NHS."