The campaign has been harsh, even virulent. Almost every day for the past month, Sir David Nicholson, the head of the NHS, has woken up to new and lurid accusations against him in the media. He has been charged with gagging whistle-blowers who wanted to expose failings in NHS care under his watch, disregarding patients to save money and, most damming of all, being directly accountable, and by implication responsible, for the unnecessary deaths of hundreds of patients at Stafford Hospital.

His refusal to resign in the wake of the Francis Report into the failings at Stafford has even earned him a rather unpleasant label in the Daily Mail: The Man with No Shame. But does he deserve the opprobrium and is he really unjustifiably clinging on to his job?

What is clear from reading the 2,000-page Francis Report into the failings at Mid Staffordshire Foundation Trust is that many organisations – and individuals within them – failed.

Uncomfortably, at its heart, is the conclusion that individual doctors and nurses at Stafford Hospital horrifically neglected their patients and were allowed to carry on doing so for years.

Managers at the hospital blithely ignored the warning signs while hospital inspectors took too long to realise what was going on. Nicholson himself never worked for the trust and only spent a year (at the beginning of the problems in 2005) at the strategic health authority responsible for overseeing it. He once visited the hospital in that time and his primary focus was attempting to merge three health authorities into one, halve the number of primary care trusts in the West Midlands and reconfigure ambulance services in the region.

In addition, the strategic health authority he was running was not directly responsible for monitoring patient care – a role that should have been performed by the Healthcare Commission and later the Care Quality Commission. After 2005 he moved to become head of the NHS – then a civil service job where he was accountable to ministers for all aspects of the NHS. Again he had no responsibility for regulating patient care or professional standards. That was the responsibility of a host of other organisations, including the General Medical Council, the Nursing and Midwifery Council and the Care Quality Commission.

Nicholson's allies argue that the leaders of those organisations are no longer in post – leaving him in the firing line, even though he is not specifically criticised in the Francis Report.

They also point out that, far from presiding over a culture of persecuting whistle-blowers, Nicholson has been at the forefront of efforts to stop NHS trusts inserting gagging clauses into contracts of former staff. Today, as Nicholson himself gives evidence to MPs, he has won backing from some surprising quarters.

Former Health Secretaries – including two who presided over the Department of Health at the time when patients were dying at Stafford Hospital – have come out in support of Nicholson. They insist that he is not responsible for what happened at Stafford and that he must not be hounded from office.

They are backed by the Chair of the Royal College of GPs – who, although a ferocious critic of the Government's health reforms – says that Nicholson is the right man to be at the helm of the NHS.

Former Labour Health Secretary Patricia Hewitt told The Independent: "I have been appalled by the campaign against David Nicholson. It is grossly unfair. The Francis Report makes clear Stafford happened because of a shocking lack of clinical and managerial governance for which the board of the hospital was responsible. David Nicholson is not."

Alan Milburn, who never worked directly with Nicholson, also defended him: "The easiest thing is to always look for the kneejerk response, put a head on a platter and then everything is solved. But it isn't, is it?

"Even a cursory reading of Francis would suggest that things went far deeper in that hospital than anything that could possibly be within David Nicholson's control."

Alan Johnson, another Labour Health Secretary, also backed Nicholson, as did Andy Burnham Labour's Shadow Health Secretary. Mr Burnham said he believed David Cameron was right to back him, adding that there was nothing in Francis to suggest that Nicholson either knew or ignored what was going on.

"The Prime Minister has said what he wants to say on David Nicholson and I think he is right," he said. "Everyone has got to look at the Francis Report, absorb its findings and take appropriate action, and everyone has got lessons to learn. The report didn't say that anybody knowingly ignored warnings."

Clare Gerada, Chair of the Royal College of GPs, said: "Any campaign that is based on a kneejerk response make me uncomfortable. We are at the most dangerous place we have been in during my career in the NHS. We are going through a period of profound transition and confusion, and we have got to have someone at the top of the organisation who understands the complexities of it. In my view, that is David Nicholson."

However, relatives' groups representing the families of those who died at Stafford Hospital vehemently disagree. Julie Bailey, 51, whose mother, Bella, died, said he should have been aware of what was going on under his watch. "If he does not resign, it sends the signal to everyone else in the NHS that you can fail in your job and get away with it," she said.

Coming to his defence: Former health secretaries on Sir David

Patricia Hewitt, Health Secretary 2005-2007: "I have been appalled by the campaign against David Nicholson and I think it is grossly unfair"

Alan Milburn Health Secretary 1999-2003: "Things went far deeper in that hospital than anything that could be within David Nicholson's control"

Andy Burnham Health Secretary 2009-2010: "As far as I could see, the report didn't say anybody knowingly ignored warnings"

Alan Johnson Health Secretary 2007-2009: "David Nicholson was part of the solution to raising quality in the NHS rather than the problem"