The detective died in a road crash in 2008 and the sergeant acted to save the dead man’s family further grief.
But Sergeant Neil Salter’s misconduct was so serious that in December last year the High Court ruled he must quit his job – overturning an earlier decision reinstating him to the reduced rank of constable.
Salter challenged the High Court’s decision in the Appeal Court but three senior Lord Justices rejected his application yesterday after having decided that the “operational integrity of the police is of fundamental importance”.
Salter, described as an “old-fashioned policeman” with an unblemished record, was investigating the death of Detective Constable Ian Morton in a road crash on October 26 2008.
Unbeknown to Det Con Morton’s partner, the night before his death he had been with his secret lover, who worked for another police force.
Salter became aware of the affair and sought to protect his dead colleague’s family.
Two mobile phones were recovered from the death crash vehicle, one of which Salter knew contained text messages which provided evidence of the affair.
Salter, who was the deputy senior investigating officer with 22 years’ service, instructed a police constable to go to a vehicle recovery centre, find the telephone and destroy it.
That officer refused and raised the matter with other senior officers, which led to Salter’s arrest.
When questioned, he admitted using the words “destroy the phone” and said he was thinking out loud.
Salter said his intention was to protect Det Con Morton’s family from discovering the affair.
The officer, who began his career with West Yorkshire Police before transferring to Dorset Police in 1991, knew the coroner conducting the inquest into the death would require all the evidence to be produced.
During a Dorset Police disciplinary hearing in August 2009, Salter admitted a disciplinary charge that he had not behaved with honesty or integrity during the investigation.
The misconduct panel required him to resign from the force and the Chief Constable agreed with its decision.
But in July 2010 Salter won an appeal before the Police Appeals Tribunal after it noted he had not acted for any personal gain but “to avoid further grief to DC Morton’s family”.
The tribunal said it was sufficient for Salter to be reduced in rank from sergeant to police constable and that he should be reinstated with Dorset Police.
It noted how Salter had been described as “a man of integrity and great loyalty – an old-fashioned policeman”.
The panel concluded the phone incident was a “one-off aberration”.
Dorset Police sought a judicial review of the decision in the High Court and Mr Justice Burnett ruled in the force’s favour.
He decided that the tribunal had applied the wrong legal test and given too much weight to Salter’s “unblemished career” and “exceptional” character.
The judge said it was true that the destruction of evidence could arise in worse circumstances than Salter’s.
“But his mitigation could not, in my judgment, tip the scales against a sanction that resulted in his leaving the police force,” the judge said.
The judge quashed the tribunal’s decision and ordered that Sgt Salter be required to resign from Dorset Police.
However, he allowed the officer leave to appeal the ruling in the Court of Appeal.
Yesterday, Lord Justice Maurice Kay, Lord Justice Stanley Burnton and Lord Justice Gross dismissed Mr Salter’s appeal.
Lord Justice Kay said: “Anyone reading the facts of the present case would feel sorry for Mr Salter.
“It is a tragic case. However, like Burnett J, I am driven to the conclusion that it had only one permissible conclusion and that the Police Appeals Tribunal erred in reaching the contrary one.”