Evidence relating to the death of Government weapons inspector David Kelly is to be kept secret for 70 years, it was reported today.

A highly unusual ruling by Lord Hutton, who chaired the inquiry into Dr Kelly's death in woods, near Southmoor, means medical records including the post-mortem report will remain classified until after all those with a direct interest in the case are dead, the Mail on Sunday said.

And a 30-year secrecy order has been placed on written records provided to Lord Hutton's inquiry which were not produced in evidence.

The Ministry of Justice said decisions on the evidence were a matter for Lord Hutton. But Liberal Democrat MP Norman Baker, who has conducted his own investigations into Dr Kelly's death, described the order as "astonishing".

Dr Kelly's body was found in woods close to his home in 2003, shortly after it was revealed that he was the source of a BBC report casting doubt on the Government's claim that Iraq had weapons of mass destruction capable of being fired within 45 minutes.

An inquest was suspended by then Lord Chancellor Lord Falconer, who ruled that Lord Hutton's inquiry could take its place. But in the event, the inquiry focused more on the question of how the BBC report came to be broadcast than on the medical explanation for Dr Kelly's death.

Lord Hutton's report in 2004 concluded that Dr Kelly killed himself by cutting an artery in his wrist. But the finding has been challenged by doctors who claim that the weapons inspector's stated injuries were not serious enough.