Police forces were yesterday advised by chief officers to halt the use of commonly employed speed detection devices because of reliability problems.

In a move that could trigger appeals against a host of speeding convictions and open the floodgates for multi-million pound compensation claims, the Association of Chief Police Officers in Scotland advised the nation's eight police forces that Vascar (Vehicle Average Speed Computer and Recorder), Police Pilot and Provida should not be used.

Strathclyde Police immediately moved to ban their use while investigations begin into the equipment's accuracy and other forces in Scotland and the UK were expected to follow suit.

The concern focuses on the effect radio transmissions from the emergency services' Airwave digital communications system has on dashboard monitors used to calculate drivers' speeds.

All police forces in England, Scotland and Wales, the British Transport Police, the Serious and Organised Crime Agency and other police agencies use the £2.9bn radio service which replaced analogue systems two years ago. The Airwave system is currently being rolled out to all fire and ambulance services.

It is also understood there is concern at the effect mobile phones, pagers, radio and TV transmitters, CB radios and amateur radios may have on the dashboard devices used to trap speeding motorists.

Legal experts say the move places under question all speeding convictions involving the detectors, posing questions about the fines levied. It also raises the spectre of compensation which may be due as a result of wrongful prosecutions and convictions.

It is estimated that British drivers have paid out £300m in speeding fines in the three years to 2007 - a figure swollen by the spread of speed cameras. One survey found that 85% of British drivers with points on their licence have received them for speeding, the equivalent to 4,598,090 motorists.

A spokesman for the Association of Chief Police Officers in Scotland (Acpos) said in a brief statement that road policing units with all forces in Scotland "have been advised of a potential issue" with Vascar, Police Pilot and Provida. Vascar, the most popular of the three, has been used in police cars for some 30 years.

"They have been advised not to use them for speed detection until the issue is resolved but to continue employing other speed detection systems.

"Despite this concern, all Scottish forces will be maintaining robust speed detection activities above and beyond those carried out by the Scottish Safety Camera Partnership."

It is understood the warning has also gone to forces south of the border but Acpos's equivalent said it was unaware of any alerts about the devices.

Strathclyde Police yesterday confirmed it was banning the use of Vascar, Police Pilot and Provida while their reliability is looked into but said in the vast majority of cases other speed monitoring equipment is used.

Inspector Andy Orr, head of road policing with the Strathclyde force, said there was a suggestion Airwave was a factor and this was being investigated.

Graham Walker, a Glasgow-based lawyer who specialises in fighting road traffic cases, said: "If they are saying that there is some kind of interference with calculations, then that could strike all the previous convictions that there have been in relation to these cases.

"It could ultimately cost the taxpayer a fortune if there are successful appeals."

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