Ministers are facing demands from more than 60 leading medical professionals to scrap or substantially rewrite the coalition government’s proposed NHS reforms.

Supported by a string of celebrities including fashion designer Dame Vivienne Westwood and comedian Russell Brand, they warned that the British public still did not support the plans.

Signatories from the medical profession include Professor Cathy Warwick, general secretary of the Royal College of Midwives and an array of consultants from hospitals across the country.

Their intervention came in a letter to the Independent timed to coincide with the return of the Health and Social Care Bill to Parliament on Tuesday, when it will be considered by the House of Lords.

Health secretary Andrew Lansley, who was forced to amend the proposals earlier this year in the teeth of widespread opposition from health professionals, is facing an attempt by peers to block or delay the Bill.

The letter insists that “both medical professionals and the British public - despite a protracted listening exercise by the government - still do not support existing plans for the NHS”.

“It is perfectly clear - as the prime minister is acutely aware - that the British public does not support the privatisation of the NHS, and it is a matter of fact that no-one ever voted for it; and so this current bill has no democratic mandate whatsoever,” it goes on.

It says that the NHS is too important valuable to be “transformed forever in this unpopular, undemocratic way”.

“We the undersigned call for the suspension of, or significant amendment of the bill in order that it can be supported by a majority of the medical profession and the British public as a whole, who pay for, support and service our great NHS.”

Other public figures to have signed the letter include actors Julie Christie and David Morrissey and novelist Will Self.

Ministers are braced for a fresh battle over the plans when peers get their first chance to debate the legislation today.

The number of peers anxious to speak on the issue has forced the Government to grant extra time for the Bill’s second reading.

Its chances of making swift progress through the Lords could be seriously damaged if former SDP leader Lord Owen succeeds in an effort to get key parts of the legislation sent to a select committee.

The House of Lords will sit earlier than usual for the second reading debate, which will continue on Wednesday when peers will also vote on Lord Owen’s amendment.

If peers agree to the crossbench peer’s demand, major elements of the Bill would go to a special committee, potentially until the end of February 2012, instead of being considered on the floor of the House.