By Alex Stevenson
The leading doctors' organisation has repeated its call for the coalition to abandon its NHS reforms.
Hamish Meldrum, chairman of council at the British Medical Association, said that ministers should either withdraw the health and social care bill or substantially amend it once again when it returns to parliament next week.
The legislation, which seeks to impose a competition dynamic on the NHS, "still poses an unacceptably high risk to the NHS in England", Dr Meldrum wrote in a letter to peers.
Health secretary Andrew Lansley has already endured major changes to the bill after an unprecedented 'listening pause' delayed its progress through the Commons for two months.
The health and social care bill now faces fresh challenges in the Lords, where it receives its second reading on Tuesday.
The BMA wants an explicit provision that the health secretary has ultimate responsibility for the NHS, assurances that increasing patient choice will not be prioritised over "fair access for all" and better scrutiny of plans for tackling failing hospitals.
Dr Meldrum wrote he fears the bill will "make it harder to create the seamless, efficient care that everyone agrees is key to future sustainability".
The BMA's call follows an open letter to members of the Lords by 400 health experts published in the Telegraph newspaper earlier this week.
The public health doctors and contractors warned that the bill would do "irreparable harm" to the NHS.
They wrote: "It ushers in a degree of marketisation and commercialisation that will fragment patient care; aggravate risks to individual patient safety; erode medical ethics and trust within the health system; widen health inequalities; waste much money on attempts to regulate and manage competition; and undermine the ability of the health system to respond effectively to communicable disease outbreaks and other public health emergencies."
Liberal Democrat peer Shirley Williams is expected to lead resistance to the health and social care bill from the government benches. She has promised "line-by-line" scrutiny of the legislation.
At her party conference in Birmingham two weeks ago she said she was most concerned by the constitutional issue of the secretary of state's responsibility for universal health provision.
Former SDP leader David Owen has emerged as an improbable ally of his former Gang of Four colleague, writing a third letter to peers warning of the constitutional perils of the bill.