An unprecedented coalition of nearly 250 doctors launches a campaign today to unseat Liberal Democrat and Conservative MPs at the next election in revenge for their backing of the controversial Health and Social Care Bill.

On the eve of the embattled legislation's final hurdle in Parliament, scores of GPs, consultants and other NHS doctors have signed a letter to The Independent on Sunday condemning the Bill as an "embarrassment to democracy" and pledging to stand as candidates against MPs who backed it.

Nick Clegg and other senior Lib Dems will be specifically targeted on polling day in 2015, as well as those in marginal seats, for betraying the wishes of activists at last week's spring conference who called for a last-minute rethink of the reforms.

But the doctors' coalition will also target vulnerable Tories in marginal seats who voted for the Bill. The Health Secretary, Andrew Lansley, who is blamed inside the Government for overseeing the reforms which have been heavily amended, is almost certain to face an electoral battle.

Yet it is the Lib Dems, who the latest poll for the IoS shows are on just 10 per cent, who face an existential threat if dozens of doctors fight in many of their 57 seats. One of the Deputy Prime Minister's Sheffield Hallam constituents, Jenny Bywaters, a retired consultant in public health, put her name forward yesterday as a possible candidate, describing the Bill as an "affront to democracy".

The 240 signatures – including 30 professors – underline the depth of anger felt by NHS frontline staff at the legislation which they claim "fundamentally undermines the founding principles" of the health service.

Dr Clive Peedell, a cancer specialist and co-chair of the NHS Consultants' Association, organised the letter and said he was overwhelmed by how many names had come forward since starting to collect signatures on Thursday evening.

Dr Peedell said they hoped to field "as many candidates as possible" at the next election, while other supporters will help with fundraising and organising the campaign. His original plan was to get 50 names but the overwhelming response suggests they could field more than that.

Pointing out that none of the major professional associations and healthcare organisations has supported the reforms, the letter says: "It is our view that coalition MPs and peers have placed the political survival of the coalition government above professional opinion, patient safety and the will of the citizens of this country.

"We are shocked by the failure of the democratic process and the facilitating role played by the Liberal Democrats in the passage of this Bill. We have therefore decided to form a coalition of healthcare professionals to take on coalition MPs at the next general election, on the non-party, independent ticket of defending the NHS."

Mr Clegg and his MPs already face anger from voters over broken promises on tuition fees and doubts over whether they have lived up to pledges to impose fairness in the tax system by targeting the richest. But the Deputy Prime Minister is now being blamed for failing to limit the wide-ranging reforms in Mr Lansley's Bill.

The doctors' letter comes as Mr Clegg and his cabinet lieutenant, Danny Alexander, enter the final stages of negotiations tomorrow with David Cameron and George Osborne over the Budget on Wednesday. The Lib Dems are fighting to impose their stamp on the measures that will restore fairness to the tax system.

Tomorrow in the House of Lords, the former SDP leader Lord Owen, now a crossbencher, will lead an amendment calling for the Bill's final stage, the third reading, to be delayed until the Government publishes the risk register – an assessment by civil servants of the consequences of introducing the legislation. Labour peers will back Lord Owen's amendment, but it is expected it will not gain enough support to block the Government forcing through the final stages of the Bill, and the legislation is expected to be granted Royal Assent on Tuesday.

Dr Peedell said: "Despite all the promises, the Liberal Democrats have failed to make a bad Bill a better Bill. Despite over 1,000 amendments, all the key policy and legal mechanisms remain in place to turn the NHS into a competitive external market, which will see increasing privatisation of provision and commissioning of care.

"This fundamentally undermines the founding principles of the NHS and will undermine professionalism and the doctor-patient relationship. We think this is scandal that is much worse than the MPs' expenses scandal because the dismantling of such a crucial and important institution will cost lives and damage the social fabric of this country."

Richard Taylor, the retired consultant who was elected as an independent MP for Wyre Forest in 2001 in protest at the downgrading of his local hospital, said he was advising the doctors. "I had no more thought of becoming an MP when I retired than I had of going to the moon, and I'm sure these doctors were the same," he said. "The doctors selected as candidates need to be popular in their own areas and they have to portray what they stand for as a vital national issue. They will need an unpopular sitting MP or one who has voted the wrong way, so they must choose their targets wisely."

Coalition MPs in the line of fire: How small majorities, national prominence and polling results have conspired to produce an early list of likely targets

Lib Dems:

Nick Clegg Lib Dem, Sheffield Hallam. 2010 majority 15,284 (29.9%)

The Liberal Democrat leader headed off a stiff challenge at the last election, but remains the top target of any "decapitation" strategy.

Simon Hughes Lib Dem, Bermondsey and Old Southwark. Majority 8,530 (19.1%)

The Lib Dem Deputy Leader has grumbled about the health Bill, but his seat is on the vulnerable list.

Lynne Featherstone Lib Dem, Hornsey and Wood Green. Majority 6,875 (12.5%)

The Home Office minister has faced down local pressure for her to oppose the Bill, insisting "there is a clear consensus that the NHS needs to change".

Jo Swinson Lib Dem, Dunbartonshire East. Majority 2,184 (4.6%)

Position as Clegg's parliamentary aide makes her a prime target; the prospect of a battle against the resurgent SNP makes Swinson even more vulnerable.

John Leech Lib Dem, Manchester Withington. Majority 1,894 (4.2%)

Has made it clear that he is not entirely happy with the Bill, but his status as a crucial Lib Dem toehold in a big city puts him in the cross-hairs.

Sarah Teather Lib Dem, Brent Central. Majority 1,345 (3%)

Declaration that "I'm afraid the Bill needs to go through" will not stabilise the education minister's wafer-thin majority.

Tories:

Jacob Rees-Mogg Con, Somerset North East. Majority 4,914 (9.6%)

A Eurosceptic, invariably described as an old-style Tory toff, a campaign against Rees-Mogg would be a strike against traditionalist Conservativism.

Chloe Smith Conservative, Norwich North. Majority 3,901 (9.2%)

Unseating the Economic Secretary to the Treasury would be a dramatic coup.

Louise Mensch Con, Corby. Majority 1,895 (3.5%)

Has not risen beyond the Culture Select Committee, but as an A-list candidate, successful author and vocal new MP, she would be a valuable scalp.

Anna Soubry Con, Broxtowe. Majority 389 (0.7%)

A prime target almost exclusively due to her tiny majority, but told constituents "people opposed to the Bill have somewhat taken advantage of people's genuine concerns and heartfelt support for the NHS".

What next for the Deputy PM? An exit route via Brussels for Nick Clegg?

If the prospect of his party becoming obliterated by a wave of angry doctors in May 2015 gets too much for Nick Clegg, he can always jump on Eurostar and head to Brussels.

Senior diplomats have begun informally circulating names for candidates for the UK's EU commissioner, a post which becomes vacant in 2014 – months before the election.

Mr Clegg, who is a former MEP and was chef de cabinet to Leon Brittan when he was Trade Commissioner in the 1990s, is being talked about as a potential candidate. Diplomatic sources believe it is a "priority" that Britain secures one of the economic portfolios – preferably the internal market commissioner post, which would defend the City from further incursions from the EU.

Baroness Ashton, the EU's representative for foreign affairs, is unlikely to seek another term. The preference for an economic role in 2014 is a recognition that Gordon Brown's enthusiasm for the UK getting the foreign affairs job was a mistake.

But a Lib Dem spokesman said: "Nick Clegg will be Deputy Prime Minister until 2015 and will lead the Liberal Democrats into the next election."