The Hutton Inquiry's finding that David Kelly committed suicide does not "hold water", and the truth is that the Government scientist must have been murdered, a senior backbench MP said today.

Following a personal investigation lasting eight months, Liberal Democrat MP Norman Baker said he did not believe that Prime Minister Tony Blair or the Government were "actually responsible for his death".

But he declined to say who he did believe was to blame, telling GMTV's The Sunday Programme that he had narrowed down his investigation to three or four possible explanations, which he was subjecting to further analysis before announcing his conclusions.

The Lewes MP revealed he had received a plausible explanation for some of the mysteries surrounding the weapons inspector's death from an unnamed individual who he said was in a position to know what happened.

He said Liberal Democrat leader Sir Menzies Campbell had given his blessing to his sleuthing, which is not being carried out under a party banner.

Mr Baker's interview comes on the day of broadcast of an edition of BBC2's The Conspiracy Files examining the theories surrounding Dr Kelly's death in July 2003 at the height of controversy over Government claims that Iraq had weapons of mass destruction.

He told GMTV: "I've concluded in my mind, beyond reasonable doubt as it were, that it's impossible for the suicide explanation to hold water.

"The medical evidence doesn't support it in any way, the psychological evidence barely supports it either and as it wasn't obviously natural causes or an accident, then you're driven to the conclusion that it must have been some sort of murder."

Dr Kelly's body was found in a wood near his Oxfordshire home shortly after he was identified as the source for a BBC report claiming the Government "sexed up" its dossier on Saddam Hussein's supposed WMD arsenal.

High-profile

Following a lengthy and high-profile inquiry, the first conclusion of Lord Hutton's report was "that Dr Kelly took his own life and that the principal cause of death was bleeding from incised wounds to his left wrist which Dr Kelly had inflicted on himself with the knife found beside his body".

But the January 2004 report - which focused primarily on the journalism of BBC correspondent Andrew Gilligan and the Government's handling of Dr Kelly as an employee - did not halt widespread speculation about supposed inconsistencies in the evidence about his death.

Some medical experts have argued that the wounds recorded in Dr Kelly's post-mortem would not cause loss of blood sufficient to kill him. Acquaintances said he did not seem suicidal in the days before his death.

Mr Baker said that Hutton's inquiry was "less rigorous" than an ordinary inquest because the Law Lord could not force witnesses to attend or require evidence to be given under oath, and yet no inquest was ever held into Dr Kelly's death.

But he did not claim to have succeeded in determining the truth himself.

"What I would say is that I have been furnished with an explanation of what happened by someone who says they know," he said.

"I've gone into that in some detail, I've met that person on a number of occasions and the information which he's given me does correspond with the facts and would explain a number of curiosities to do with the particular case.

"I'm seeking to test it to destruction as I have done with other potential explanations. I haven't managed to disprove it yet... and indeed the evidence I've managed to accumulate has provided circumstantial support for that explanation.

"I'm looking at that explanation, I'm looking at two or three others which I've not yet disproved and, as and when I'm able to state with confidence what I believe happened, then I will say so."

He added: "I don't believe that Prime Minister and the politicians and the Government were responsible for what happened to David Kelly.

"I believe they treated him shamefully and I believe that they treated him callously in that they deliberately leaked his name to the press and they were quite happy to offer him up as fodder in some sort of Soviet-style Foreign Affairs Committee hearing in order to discredit Andrew Gilligan and the BBC.

"But I don't believe they were actually responsible for his death."