He was supposed to have died by his own hand when his body was found in an Oxfordshire wood in 2003, after he had been caught up in the tangle between the Government and the BBC over the allegation that No 10 "sexed up" the intelligence claiming that Saddam Hussein had weapons of mass destruction.

The claims that Britain's senior expert on germ warfare had been killed by "dark actors" from some foreign government – or even by members of our own security services – were supposed to have been laid to rest by the 2004 Hutton Inquiry into Dr Kelly's death. It concluded that the scientist had died from a haemorrhage caused by a severed wrist artery with two contributory factors: poisoning by 29 co-proxamol pain-killing tablets and undiagnosed coronary artery atherosclerosis.

It was a suicide verdict some people did not accept. Some of those sceptics were wild conspiracy theorists, but other more respectable voices have raised questions.

In January this year, Lord Hutton ordered that all files relating to Dr Kelly's post-mortem – including the autopsy report, unpublished medical and scientific records and photographs of the body – should remain secret for 70 years. The judge suggested that his intention was to avoid further distress to the family. But the move fuelled the conviction of sceptics that something was being hidden.

And in the last two months, a rash of disbelieving newspaper articles, predominantly in the Daily Mail, but also picked up by The Times, have ratcheted up pressure on the Government to re-open investigations into David Kelly's death.

In June, Richard Spertzel, the former head of the UN Biological Section, who worked with Dr Kelly in Iraq in the 1990s, wrote to the Attorney General, Dominic Grieve, claiming that Dr Kelly had been told he was on a "hitlist" in the final years of his life. Then Graham Coe, the detective who found Dr Kelly's body, claimed in an interview (with the Mail on Sunday) that there was less blood found at the scene than was recorded by the Hutton inquiry. He also revealed that, contrary to the evidence he had given Hutton, a third man (a member of the security services, in the eyes of the conspiracy theorists) was with him and his partner when they found the body. (Coe did conclude: "In my view he [Kelly] took his own life. Only he will know why he did that.")

Earlier this month, nine doctors wrote an open letter calling for "a detailed investigation of all the medical circumstances" and alleging that the Hutton Inquiry's procedures and conclusions were "unsatisfactory". The doctors wrote that it was "extremely unlikely that the primary cause of death would or could have been haemorrhage from a severed ulnar artery in one wrist without any evidence of a blood-clotting deficiency."

They called for a "proper inquest", and were supported by a retired pathologist, Jennifer Dyson, who insisted that, had there been normal inquest, a coroner would probably have recorded an open verdict in the absence of absolute proof that suicide was intended.

Then the former Conservative Party leader Lord Howard called for a full inquest into Dr Kelly's death, and the Justice Secretary Ken Clarke – the only minister who could overturn Lord Hutton's decision to impose a 70-year secrecy order – met the Attorney General to discuss the issue.

Mr Grieve appears to have little desire to reopen the case. His spokesman said yesterday: "The Attorney General has no investigative function. Whilst he could ask for the papers [impounded under Hutton's 70-year secrecy order] it would be extremely unusual for him to take a proactive step of that kind." Yet the pressure for a new investigation continues. Below, we weigh up the evidence under consideration.

Claim: "Dr Kelly could not have bled to death"

David Kelly's death certificate states that he died from loss of blood. But the nine letter-writing doctors, who included some with expertise in vascular surgery and forensic medicine, challenge that verdict. The blood vessel served was the ulnar artery, the second in the wrist, which one of them described as the width of a matchstick. To die from a haemorrhage Dr Kelly would have had to lose 2,700ml (almost five pints) of blood. "It was impossible for 2,700ml of blood to have been lost through this small artery," the doctors wrote. Moreover, they added, the artery would probably have retracted on being severed and clotting would have ceased the flow.

The other factor raised by the nine doctors was the lack of blood where the body was found. The two paramedics called to Dr Kelly's body have said there was not enough blood at the spot to justify the belief that he died from blood loss.

The suppressed post-mortem documents mean there is no answer to why the blood-stained leaf litter and soil was not collected. However the doctors were challenged by Dr Andrew Davison, a forensic pathologist at Cardiff University, who accused the nine of a lack of relevant autopsy or forensic pathology expertise: "At an outdoor scene, where blood can seep into the ground, I would not expect to be able to make an accurate estimate of blood lost, and there is no way of measuring the blood remaining in the great vessels post-mortem."

Other parts of their science are also disputed. A surgeon specialising in wrist injuries complained that the doctors made mistakes in their letter. "The ulnar artery is not a minor artery, but the main artery supplying the hand and is substantially bigger than a matchstick," Dr LC Bainbridge, a consultant hand surgeon, wrote to The Times. Arteries' ability to retract, constrict and close is affected by age, and "even a small amount of hardening of the arteries can be sufficient to prevent enough constriction to stop the bleeding". Constriction also relied on there being a clean cut to the artery, not a ragged one as in Dr Kelly's case.

Claim: "Kelly's dose of painkillers was non-fatal"

Lord Hutton concluded: "It is probable that the ingestion of an excess amount of co-proxamol tablets coupled with apparently clinically silent coronary artery disease would both have played a part in bringing about death more certainly and more rapidly than would have otherwise been the case."

Some doctors disagree, saying that the number of pills that Dr Kelly had consumed was not enough to cause death. Co-proxamol is a combination of two drugs, dextropropoxyphene and paracetamol, both of which are highly toxic in overdose. In Dr Kelly's blood the concentration of dextropropoxyphene was at the lower end of the range that has been measured in people who have used co-proxamol successfully to commit suicide.

Jennifer Dyson, the retired pathologist, suggested that the combination of stress, blood loss and overdose could have produced a heart attack; the autopsy showed Dr Kelly was suffering from cardiovascular problems he did not know about. Another forensic pathologist, Chris Milroy of Sheffield University, suggests that Dr Kelly's heart condition may have made it hard for him to survive any significant degree of blood loss. And Professor Robert Forrest, a toxicologist and the former President of the Forensic Science Society, concludes: "I've no doubt that the cause of David Kelly's death was a combination of blood loss, heart disease and an overdose of co-proxamol... it is important that all of them interacted to lead to the death."

Claim: "A suicide verdict didn't make sense from a psychiatric point of view"

Lord Hutton's verdict of suicide was largely based on evidence by Professor Keith Hawton, director of the Centre for Suicide Research at Oxford University's Department of Psychiatry. Professor Hawton spoke to Dr Kelly's widow and daughters, read his last emails and watched a recording of his interrogation by a committee of MPs. Dr Kelly, he said was not "mentally ill", a factor often linked to suicide, but there were very significant pressures upon him.

But another leading expert on suicide, Colin Pritchard, emeritus professor at the University of Southampton, last week expressed concern about how fully Prof Hawton was questioned by Lord Hutton. Insufficient weight had been placed on Dr Kelly's arrangement to see his daughter Rachel on the evening of his death, Prof Pritchard claimed, and given the quality of the relationship between father and daughter, Dr Kelly would have left an apologetic note.

Crucially, Prof Pritchard said, there was no evidence of "intent to die" by Dr Kelly, which is essential for any suicide verdict. "No coroner in the land would say anything other than 'Open verdict'."

However, the BBC journalist Tom Mangold, a friend of Kelly's, is firmly of the opinion that he killed himself, and that the conspiracy theorists have yet to identify motive, perpetrators or opportunity. Mr Mangold says for the conspiracy theories to be correct, David Kelly was somehow kidnapped unseen from his house in a small village while his wife was present, frog-marched into the woods, released (a friend saw him walking alone) and re-captured, before having his wrist cut and 29 tablets forced down his throat without leaving a mark; there would have to subsequently be a cover-up between local police, Special Branch, MI5, MI6 and some central government employees.

Mr Mangold's conclusion: "I believe that David killed himself because he learned, a few hours before he took this fatal step, that lies he had told to MPs on the Foreign Affairs Committee hearing on 15 July would be exposed. He had, foolishly, denied having contact with the BBC Newsnight journalist Susan Watts. She had taped the interview and the BBC was about to reveal this. I believe David learned of this impending disaster on the morning of his death... With that knowledge came an instant awareness that his honour and integrity would be besmirched... His world collapsed."

Claim: Oddities and inconsistencies in eyewitness accounts

Why did Graham Coe, the detective who found Dr Kelly's body, not tell Hutton that there was a third suited man with him and his partner DC Colin Shields when the body was discovered, as some eyewitnesses had suggested. Why has he subsequently admitted this? And why does he refuse to name him?

How did Dr Kelly cut his left wrist if, as friends said, he had damaged his right arm to such a degree that he struggled cutting steak?

Why was the ulnar artery severed rather than the radial, which is how the cut would "naturally" have been made, from left to right, with the right hand? Could this suggest the cut was made by a third person?

Why were there no fingerprints on the knife when Dr Kelly was not wearing gloves? Nor on the bottle from which he supposedly drank to swallow the tablets? Why was that fact not disclosed to Hutton, but only later through a Freedom of Information request?

Why did the helicopter which passed over the scene with heat-seeking equipment not detect the body soon after death – a piece of information obtained using the Freedom of Information Act five years after the Hutton Inquiry ended?

What explains the discrepancy between the account of the position of the body given by the dog handler who discovered it and the paramedics when they arrived? Did someone move the body? Did Dr Kelly die where his body was found?

Why did the head of the investigation into Dr Kelly's death, Superintendent Alan Young of Thames Valley Police, not give evidence to Hutton?

Did the police and three officers from MI5's Technical Assessment Unit strip the wallpaper at Dr Kelly's home in the hours after he was reported missing – but before his body was found? Had Dr Kelly written 40,000 words of a book on Iraq and biological warfare which they took away? Where are his computers now?

Why did Lord Hutton place a 70-year embargo on release of the post-mortem documents?

*****

The answers to many of those questions could be mundane and inconsequential. Those who insist that Dr Kelly was murdered by the Iraqis – or by MI5 to prevent him from disclosing that Britain helped Saddam develop biological weapons in the 1980s – or who have developed some other far-fetched conspiratorial fantasy, could well be disappointed. The question remains as to whether a normal inquest would have recorded a more enigmatic Open Verdict.

What ministers must now consider is whether a full-blown inquest would achieve much. Politically, it would provide another stick with which to beat Tony Blair. Would it sate the sceptics?

Britain has a history of long, expensive public hearings – from the Hillsborough Disaster inquiry to the inquest into the death of Princess Diana and the Saville investigation into Bloody Sunday – which do little but confirm most people in their pre-existing views and prejudices. What political catharsis would be achieved by raking over the detail of Dr Kelly's death and coming to more exhaustive but almost certainly equally inconclusive findings?

Belfast Telegraph