A police force has banned its advanced drivers from breaking the speed limit "at their own initiative" in non-emergency situations after widespread criticism of a Pc who sped along a motorway at 159mph.

West Mercia Constabulary said it had now clarified the instructions given to its officers after Wednesday's decision by a magistrate to clear Telford-based Pc Mark Milton of dangerous driving and speeding.

A police spokesman said: "Our advanced drivers are trained to an extremely high standard to ensure the safety of the public, themselves and their colleagues.

"We expect them to exercise professional judgement and common sense at all times and, overwhelmingly, this is what they do.

"When reacting to operational incidents which require an emergency response, officers will continue to drive in accordance with their training at speeds that are safe and appropriate for the prevailing road conditions."

The West Mercia force also plans to consult with colleagues in other areas to consider if national guidance is required in such circumstances.

The force also explained its decision to investigate 38-year-old Pc Milton, who came under fire from safety campaigners for the " eyewatering" speeds he reached while putting a 3.2-litre Vauxhall Vectra through its paces in December, 2003 on the M54 in Shropshire.

A spokesman said: "The investigation into this matter was initiated by West Mercia Constabulary because the recorded speeds appeared to be wildly excessive."