The head of the professional body for doctors has warned David Cameron that the NHS must not be undermined as a result of radical reforms.

Dr Clare Gerada, chair of the Royal College of General Practitioners has written to the prime minister outlining “serious concerns” regarding aspects of the proposals and offered a number of recommendations to make the changes more palatable.

Key to the RCGP suggestions were that the NHS must remain a comprehensive service that was available to all, free at the point of use and based on clinical need, not on the ability to pay.

The move comes after deputy prime minister Nick Clegg threatened to veto the reforms unless they were substantially improved.

The government’s so-called “pause” in the passage of the bill through Parliament to listen to concerns has sparked tensions within the Conservative-Liberal Democrat coalition and opposition from unions, charities and some royal colleges.

Dissent over the reforms saw nurses deliver an unprecedented vote of no confidence in health secretary Andrew Lansley last month.

The RCGP letter details nine recommendations over issues ranging from the need for clarity about the implications of EU competition law, to an “absolute” assurance that the bill would not force doctors to breach their duty of confidentiality.

Other recommendations include making sure providers cannot charge patients for services that are currently free and that consortia remain publicly accountable for all commissioning decisions.

The RCGP also called for the proposal to abolish practice boundaries to be revised.

The recommendations conclude: “The future NHS must build on the strengths and values of today’s health service, in particular building on the strengths of general practice.

“The benefits of modern general practice are well documented, with significant evidence that a good relationship with a GP, preferably over several years, is associated with better care, more appropriate care, better health, and much lower health costs.”

Labour’s shadow health secretary John Healey MP said: “The letter is a red card for David Cameron’s NHS plans and reinforces Labour’s warnings.”

“From competition law to charging patients, GPs are making it clear they don’t want the Tories’ free market NHS and the prime minister must now make radical changes to his health plans in order to regain the trust of NHS professionals”.