Britain's medical establishment has decided to toughen its stance against the coalition's controversial NHS shakeup. All but one of the 20 medical colleges that represent medical professionals have come out against the government's proposals to change the service.

The Academy of Medical Royal Colleges (AoMRC) agreed the move on Tuesday when its members, who represent all the different medical specialities, said it held a "full, long" debate on the bill.

The Guardian has obtained a draft statement that says: "The Medical Royal Colleges and Faculties of the AoMRC continue to have significant concerns over a number of aspects of the health bill and are disappointed that more progress has not been made in directly addressing the issues we have raised."

The medical bodies say that "unless the proposals are modified the academy believes that bill may widen rather than lessen health inequalities and that unnecessary competition will undermine the provision of high quality integrated care to patients.

"The Academy and Medical Royal Colleges are not able to support the bill as it currently stands.

"The academy is deeply concerned that the upheaval caused by the changes in the bill will distract the NHS from the huge task of meeting the current financial challenges."

However, the Royal College of Surgeons will continue to support the "aims of the reforms", saying that these would help "to modernise the health care system".

Unlike the full-throated opposition of the British Medical Association, the Royal College of Nursing and the Royal College of Midwives, the draft statement says "the academy and colleges retain these concerns but they will work with the government and NHS organisations to ensure that the NHS provides the best possible care to patients should the bill become law".

The move follows decisions by the BMA, RCN and RCM, which together represent the bulk of the NHS's medical workforce, to call for the bill to be dropped. The NHS Confederation, which speaks for 95% of the NHS's employers such as hospitals and ambulance services, has voiced concern at the lack of clinical support for the bill.

The legislation, which is due to return to the House of Lords early next month, would involve a radical restructuring of the NHS in England from April 2013, resulting in newly formed groups of GPs, called clinical commissioning groups, replacing NHS primary care trusts as the bodies that control £60bn of patient treatment budgets.

Most of the academy's members are also due to attend an unprecedented summit on Thursday evening, called by BMA leader Dr Hamish Meldrum, in an effort to further galvanise medical opposition to the bill. The RCN, which represents about 300,000 nurses in the NHS, will also attend. The RCN's chief executive and general secretary, Dr Peter Carter, has condemned health secretary, Andrew Lansley, for refusing to change the substance of his plans in response to detailed concerns it has raised over many months.

However, although Wednesday's statement will present a united front, behind the scenes there is a range of divergent views.

While the BMA, RCN and RCM want the bill dropped entirely, other colleges have "significant concerns" that could be addressed through changes to it, while the Royal College of Surgeons of England (RCSE) has many fewer objections.

Some in the NHS claim that the surgeons' position stems in part from Lansley's bid to allow NHS foundation trust hospitals to earn as much as 49% of their revenue from treating private patients. It is this plan that critics such as the RCN and Labour's shadow health secretary, Andy Burnham, have warned would turn the NHS into a two-tier system in which those who can pay get preferential treatment.