A judge said a controversial decision to dismiss police proceedings brought against Chief Inspector Alan McArthur, head of Devon and Cornwall police firearms unit, was the result of a "misdirection in law".
In what amounts to a significant victory for Mr Fitzgerald Hay's family and the independent Police Complaints Authority, the judge overturned a decision of the Chief Constable of Wiltshire, Walter Girven, in May to halt a police internal disciplinary hearing on the grounds that the proceedings were "an abuse of process".
Mr Justice Sedley ruled: "On the view which I take of the law and the fact, the only decision open to Mr Girven was that there was no unfairness in proceeding with the charge."
Ch Insp McArthur was in charge of a nine-strong firearms team which laid siege to Mr Fitzgerald Hay's home in Diptford, Devon, in October 1993.
An inquest jury in December last year returned a verdict of lawful killing after hearing that the farmer, who had shot dead a police dog, was killed when three officers fired simultaneously within two minutes of arriving at the scene.
The officers told the inquest they were convinced that Mr Fitzgerald Hay, 39, was about to turn his handgun on them.
But family members later accused the police of "over- reacting" and said if they had checked the farmer's background they would have realised that he was mentally unstable.
The judge yesterday refused to interfere with Mr Evans's decision to allow Superintendent Roger Mechan, who had been sent to take overall command of the siege operation, to resign from the force on health grounds.Reuse content