The motorists had been banned from driving and in some cases fined but their convictions have now been overturned.

About 10,500 results are now under review after Randox Testing Services allegedly manipulated the data.

The National Police Chiefs’ Council (NPCC) said it was the “most serious breach” of forensic science standards.

Another 50 drug-driving cases have been dropped following the alleged manipulation at the company’s laboratory in Manchester.

Randox said in a statement it acted as its own whistleblower after it discovered manipulation by staff in January 2017.

Police last year suspended all contracts with the firm, which is used by 42 of the UK’s police forces, and two men have been arrested by Greater Manchester Police, on suspicion of perverting the course of justice.

A further six people have been interviewed under caution, one of whom is under investigation as part of a criminal inquiry.

Hudgell Solicitors is representing 35 people who have had their convictions quashed as well as others seeking damages.

Head of civil liberties, Andrew Petherbridge, said: “This is a national scandal which has had a devastating impact on the lives of the many people we are representing.

“People have lost their driving licences, and as a result lost their employment, struggled to pay bills such as mortgages and rents, and some have been unable to travel to see their families and children.”