Attorney General Dominic Grieve rules out asking the High Court to order an inquest into the death in 2003 of weapons expert Dr David Kelly.
Mr Grieve said: “Having given all the material that’s been sent to me the most careful consideration, I’ve concluded that the evidence that Dr Kelly took his own life is overwhelmingly strong.
“Further, there is nothing I’ve seen that supports any allegation that Dr Kelly was murdered or that his death was the subject of any kind of conspiracy or cover-up.
“In my view, no purpose would be served by my making an application to the High Court for an inquest, and indeed I have no reasonable basis for doing so.
“There is no evidence I’ve seen that would suggest any other explanation, or that would suggest any cover-up or conspiracy whatsoever,” he said.
He insisted all the evidence from the careful forensic examination of the scene and his own detailed review supports the view that Dr Kelly committed suicide.
This Government is complicit in a determined and concerted cover-up. Dr Stephen Frost
Mr Grieve also stressed he had not been pressurised by the Government when considering his decision.
Last month, the Prime Minister David Cameron suggested a full inquest was unnecessary, saying the Hutton report into the Government weapons inspector’s death had been “fairly clear”.
But a group of campaigning doctors, led by Dr Stephen Frost, accused the Government of being “complicit in a determined and concerted cover-up”, saying they would now seek a judicial review of Mr Grieve’s decision.
But the decision has not moved the opinion of Lib Dem minister Norman Baker who devoted a year of his life to writing a book questioning the investigation.
In a statement he said: “I have not been actively involved in this area for some time, though I should say that I have seen nothing in the years that have passed to cause me to doubt the central conclusions of my book.
“I accept of course that it is the Attorney General who speaks for the government on this issue.”
The scientist’s body was found in woods close to his Oxfordshire home in 2003, shortly after he was revealed as the source of a BBC report questioning the accuracy of a Government dossier arguing the case for war in Iraq.
The Hutton Inquiry in 2004 found that Dr Kelly committed suicide, and the then Justice Secretary, Lord Falconer, ruled the inquiry could take the place of an inquest in the coroner’s court.
But the doctors pointed out that Lord Hutton spent only half a day of his 24-day inquiry considering the cause of Dr Kelly’s death.
They have denounced the Hutton report as a “whitewash” which “failed adequately to address the cause of death itself and the manner of death” and also claimed that a coroner would not have reached the verdict of suicide on the basis of evidence heard by Hutton.
Dr Frost said: “The coroner is required to hear evidence which constitutes proof beyond reasonable doubt that the deceased killed himself and that he intended to kill himself, before he may return a verdict of suicide.
“Lord Hutton did not hear evidence which came near to satisfying that test.
“It is therefore very surprising and perplexing that the Attorney General today supports those who wish to deny Dr Kelly a proper inquest.
This is clearly a political decision when it should have been a decision based solely on the law. This Government has now revealed itself to be complicit in a determined and concerted cover-up.”
He condemned the “deeply flawed” decision, saying it had “no basis in law”, and called for Mr Grieve to resign.
“As a lawyer, his position as Attorney General is now untenable and he will no doubt be subject to reasonable demands that he resign,” Dr Frost said.
“The continuing cover-up of the truth of what happened is a national disgrace and should be of concern to all British citizens.”
The group is now planning to challenge the Attorney General’s decision via a judicial review.
Dr Frost added: “A proper inquest into the suspicious death of any British citizen is required by the laws of this country.
“Everyone now knows that the Hutton Inquiry, which purported to fulfil the coronial requirement, was a woefully inadequate instrument for investigating this most important death, especially given the highly controversial context of illegal war in which the death of this loyal and brilliant public servant took place.”