A Sussex MP claims Government scientist Dr David Kelly may have been assassinated.

Norman Baker, Liberal Democrat MP for Lewes, suspects British and American security services could have played a part in the weapons expert's death in July 2003.

The senior backbencher, whose persistent questioning led to the resignation of Peter Mandelson from the Cabinet over the Hinduja passport affair, has tabled about 30 Parliamentary questions about coroners' procedures and suicide methods to get to "the truth" about Dr Kelly, who is believed to have killed himself after being exposed as a whistleblower.

Mr Baker said: "I have grave doubts over whether he committed suicide due to medical and other evidence.

The explanation given for suicide is barely credible. If suicide is not the explanation then assassination is."

He did not believe Government ministers were responsible because they "had nothing to gain" from Dr Kelly's death.

He said: "That leaves the possibility of the security services."

Mr Baker's private investigation has been criticised by a close friend of Dr Kelly, who described it as a complete waste of time.

Journalist and author Tom Mangold rejected the possibility Dr Kelly was murdered as ludicrous.

He said: "There is not a shadow of doubt in my mind that he committed suicide."

The official account of events said Dr Kelly killed himself five miles from his Oxfordshire home by severing the ulnar artery in his wrist "avoiding the main artery on top", according to Mr Baker.

A Parliamentary answer suggested Dr Kelly was the only person in the country to die after cutting his wrist in this way in 2003.

Mr Baker said a number of health professionals had told him it was "well nigh impossible" for someone to kill themselves in the way suggested.

He also said although Dr Kelly had supposedly taken 29 painkillers, only "a quarter of one tablet" was found in his stomach.

The MP, who is convinced Dr Kelly did not have the intent to take his life, said the Hutton Inquiry, set up to look into the circumstances surrounding the death, had failed to ask the "obvious questions".

The report concluded no one could have contemplated Dr Kelly would take his life as a result of the pressures he felt after he was identified as the source behind BBC reports accusing the Government of "sexing up" evidence of weapons of mass destruction in Iraq.