Forty-one convictions for drug-driving have been quashed after evidence was re-examined.
It comes amid an investigation into alleged data tampering at a forensics lab, the National Police Chiefs’ Council has said.
The NPCC’s forensics lead, Chief Constable James Vaughn, said on Thursday that more than 50 drug-driving investigations were dropped, with some 2,700 results re-analysed so far.
A further 41 drug-driving cases which had already resulted in convictions or guilty pleas have since been reopened and overturned, he added.
The retesting of more than 10,500 cases opened since 2014 came after allegations emerged that scientists at a Randox Testing Services (RTS) site in Manchester had manipulated forensics data.
The results of the investigation were described as a “national scandal” with a “devastating impact” by a lawyer seeking damages for 35 of the 40.
“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,” added Andrew Petherbridge, of Hudgell Solicitors.
One of those is Luke Pearson, a scaffolder from Manchester who lost his job when he accepted a 12-month driving ban and a fine before having his case overturned in February, according to the firm.
“I think it is disgusting that this has been able to happen to so many people, and it was devastating to me,” the 26-year-old said.
“It all put a strain on life, and on my relationship with my girlfriend as I was the main earner and we struggled with bills and rent.
“I was only an occasional, light cannabis user, but when the police tell you that science says you are guilty you can’t argue.”
Two men, aged 31 and 47, were arrested on suspicion of perverting the course of justice by Greater Manchester Police and have been bailed until January.
Six more people have been interviewed under police caution with one remaining under investigation.
The major investigation into the laboratory used by 42 of the UK’s 43 forces was launched in January 2017.
It found around 3% of cases reanalysed have been dropped or overturned. All of these were brought over drug-driving allegations.
A further case referred to the appeals court saw a sentenced reduced, one appeal unsuccessful with a fourth pending, Chief Constable Vaughn said.
He believes the botched results are due to the manipulation of test results rather than samples being tampered with but was unable to guarantee samples’ fidelity at this stage.
“We can’t be fully sure, that’s part of the investigation into Randox,” he added.
Of the 40 cases reopened, they were all dropped using powers under the Magistrates’ Courts Act.
All had received driving bans or fines but had not been sent to prison, the chief constable said.
Retesting is expected to continue into December 2019 and has been slower than expected partly due to an existing shortage of forensic testers which has been exacerbated by the scandal.
He added: “We have a perfect storm of a chronically saturated market, now you have one less accredited provider in the market and now you have 10,500 new cases for retesting.”
More than 10% of the most serious cases still must be retested, with thousands still needing fresh analysis.