A police constable who reached 159mph while "familiarising himself" with a new patrol car was yesterday cleared of dangerous driving and speeding after a judge criticised the decision to prosecute him.

District Judge Bruce Morgan, sitting at Ludlow Magistrates' Court, acquitted PC Mark Milton after describing the 38-year-old as the "creme de la creme" of police drivers.

The court had heard that the officer, who is trained in advanced driving and the use of firearms, was recorded travelling at 159mph on the M54 near Telford, Shropshire, in the early hours of December 5, 2003.

Giving his verdicts, Mr Morgan said: "I can't help but see the irony that those that brought this prosecution are those very people who have purchased cars that go at this speed and paid for him (the defendant) to go to learn to drive at these speeds."

PC Milton, from Bratton, Telford, left the court with his wife without comment other than to say he was relieved at the outcome of the case.

The officer told the court at a previous hearing that he had taken the newly-commissioned, unmarked 3.2-litre GSI Vauxhall Vectra on to the road to assess its capabilities.

Criticising the investigation into the alleged offences, Mr Morgan told the court that he accepted that PC Milton had driven at "eye-watering" speeds while on duty.

But the judge expressed deep concern at West Mercia Constabulary's "total lack of policy" on when and where police officers should practise driving at very high speeds.

Mr Morgan noted that two police officers who gave evidence for the prosecution, including West Mercia Police's senior driving instructor, had declined to classify the defendant's driving as dangerous.

He said: "At the end of the day, those who get their (advanced level driving) certificates are the creme de la creme of police drivers"

Speaking after the case, a police spokesman revealed that the West Mercia force was clarifying the guidance issued to advanced drivers.

"Officers are trained to the highest standard and there are exemptions in law in relation to the speed limit," he said. "However, any breach of a speed limit must be justifiable on every occasion a speed limit is exceeded."

Referring to the prosecution brought against PC Milton, the spokesman said: "The Crown Prosecution Service determined that a prosecution was appropriate."

Kevin Clinton, of the Royal Society for the Prevention of Accidents, said he did not believe doing 159mph on a public road could ever be justified.

"We are shocked that speeds of 159mph are not regarded as dangerous by the court," he said.

The Police Federation defended the driving of PC Milton, who is also known to have travelled at 120mph in a 60mph zone and at more than 60mph in a 30mph zone.

Inspector Keith Howes, the federation's divisional official for the Telford area, said: "PC Milton was driving in accordance with his training, honing his skills while possible and testing the vehicle's capabilities so that if he was required on an urgent call he would be driving safely."

However, RAC spokesman Philip Hale said: "Most ordinary motorists will just interpret this as 'one rule for him, another for everyone else'.

"Regardless of their training standards or experience, we must question a policy that asks or allows officers to 'test' their vehicles at these speeds on public roads."