David Kelly's body was found near his Oxfordshire home in 2003
Six doctors are taking legal action to demand a formal inquest into the death of government scientist Dr David Kelly.
They say Lord Hutton's conclusion that he killed himself is flawed and have approached the attorney general to get the issue considered at the High Court.
Dr Kelly's body was found in 2003 after he was exposed as the source of a BBC story on the grounds for war in Iraq.
But Michael Powers QC said there was insufficient evidence to prove beyond reasonable doubt he killed himself.
Instead of a coroner's inquest, the then prime minister Tony Blair asked Lord Hutton to investigate the death.
Lord Hutton concluded he bled to death as a result of cutting his wrist and taking an overdose of painkillers.
But Dr Powers, a former assistant coroner, said the cuts would not have caused him to bleed to death and the dose of co-proxamol in Dr Kelly's body was normal.
He said: "Suicide cannot be presumed it has to be proven. From the evidence that we have as to the circumstances of his death, in particular the aspect of haemorrhage, we do not believe that there was sufficient evidence to prove beyond reasonable doubt that he killed himself.
He said that there was not enough information to determine whether Dr Kelly was murdered or killed himself.
He added that the inquest should not have been left to Lord Hutton because he is not a coroner.
"There are many times in political life that the country needs to have an answer and the desire to have an answer overwhelms the desire to get the right answer," he said.
"I have no doubt that many of us when we read about this thought that he had killed himself. But you cannot be certain.
"Everyone's death is significant. This death had a significance which was greater and I feel that the process of the investigation of death ought to have been a thorough one. That was not provided for him."
Dr Powers and five other experts have instructed solicitors Leigh Day and Co to approach Attorney General Baroness Scotland.
The experts are trauma surgeon David Halpin, epidemiologist Andrew Rouse, surgeon Martin Birnstingl, radiologist Stephen Frost, and Chris Burns-Cox who specialises in internal general medicine.
Mr Halpin said: "We don't believe that anyone, high profile or not, should go without an inquest in this country. Any unnatural death has to be investigated properly. This has not."
He said his personal view was that it was "very likely" Dr Kelly was assassinated.
He said MP Norman Baker had uncovered information showing there were no fingerprints on the knife the scientist apparently used to slash his wrist, even though he was not wearing gloves.
Dr Powers said it was never made public how much blood Dr Kelly had actually lost and although there was very little co-proxamol in his body, three packets of 10 were found nearby with just one pill left.