A group of doctors has lodged papers to seek judicial review of the Attorney General's refusal to give his consent for an inquest into the death of Dr David Kelly.
Dr Kelly, the Government weapons inspector, who died in July 2003 aged 59, was judged to have committed suicide in a report published by Lord Hutton following a public inquiry.
The Attorney General, Dominic Grieve, concluded in June this year that there was no possibility that any inquest would reach any other verdict than suicide.
Papers applying for permission to seek judicial review were lodged at London's High Court this afternoon in the name of Dr David Halpin, one of the four doctors.
Dr Halpin recently said, as he asked the public to contribute funds for the legal challenge: "Britain has great potential for good but many people know it is now mired in mendacity.
"They must help the doctors get light into the dark corner of the Dr Kelly cover-up. Truth must out."
The Attorney General ruled out an inquest after telling Parliament the evidence that Dr Kelly killed himself was "overwhelmingly strong".
The doctors say they are acting because there are still unanswered questions about Dr Kelly's death.
Today was the legal deadline for launching their judicial review application.
An inquest into the death began as a matter of routine after Dr Kelly's body was found in woods close to his home in Oxfordshire, but was replaced by a public inquiry chaired by Lord Hutton.
The weapons inspector was judged in the Hutton report to have killed himself after slashing his wrist with a blunt pruning knife and overdosing on painkillers.