A motorist scared at being followed by a car on the motorway called 999 to be told it was two plain clothed police officers in the car behind him.
Strathclyde Police has been heavily criticised by the Police Complaints Commissioner for Scotland for the way it pursued the man for seven miles in an unmarked car.
In a decision released by the commissioner on Thursday, the man claimed that the unmarked car following him on the motorway last January started flashing its headlights at him.
The report found that the motorist was being pursued by the officers because they thought he was driving dangerously, but he "did not know that the car was a police car".
In his findings, the commissioner Professor John McNeill found that the unnamed driver became "increasingly concerned at his being followed by a car containing two males and eventually he telephoned 999 whilst driving in order to report the matter".
He added: "The applicant drove for several minutes until the 999 operator was able to advise him that the car following him was in fact a police car. By the time the applicant stopped his car he had driven for around seven miles of motorway from the point at which he claims to have first become aware of the car being driven behind him."
The commissioner found that the force had displayed a "poor" handling of three of the four complaints made by the man, who was charged with road traffic offences after pulling into the hard shoulder once the police operator informed him it was an unmarked car pursuing him.
Professor McNeill cited guidance which prohibits police form using of unmarked vehicles which do not have any audible or visual warning equipment. He went on to recommend that Strathclyde Police apologises to the man for the pursuit in the unmarked vehicle and for having been stopped when the plain clothes officers lacked the power to do so.
The commissioner also asked the force to respond to concerns raised by the motorist in his complaints about his personal safety during questioning in the unmarked vehicle, which the detective constable and detective sergeant had stopped on the hard shoulder of the motorway.
Professor McNeill also rejected a complaint from the motorist about the detective constable being uncivil towards him.
Deputy Chief Constable Campbell Corrigan said: "The commissioner's report makes some points about how we handled this particular complaint. We are examining these points and where appropriate we will ensure that they are acted upon.
"However, we cannot and will not accept that the officers acted illegally or without any legal basis. We believe this assertion to be wrong and we will be writing to the commissioner to make this point clear. The officers did act outwith ACPO guidelines, but I would ask the public to stop for a moment and consider why they did so.
"They saw someone driving erratically on a busy road and they believed that this represented a risk to other drivers. Their first concern was the safety of the public. I'm sure that the public would be more alarmed if they sat back and had not taken any action."
He added: "We consistently tell our officers that we believe that it is their duty, first and foremost, to keep people safe. That is what those officers were doing and that is what I would expect every officer to do. It is a source of great regret that they have had their reputations wrongly tarnished in this way."
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