An investigation into alleged data manipulation at a forensics laboratory used by all of Yorkshire's police forces has now identified more than 10,000 cases nationally which "may have been affected".
The National Police Chiefs' Council has said three-quarters of the cases involving Manchester-based Randox Testing Services, across 42 police forces, were traffic offences such as drug driving, with the rest including violent crime, sexual offences and unexplained deaths.
Retests have so far found no impact on cases of sexual offence cases, violence or homicide, the NPCC said.
But a number of retests had resulted in drug driving cases being discontinued and two road deaths had been referred to the Court of Appeal.
In March, The Yorkshire Post revealed 201 of the original 484 cases initially uncovered as being in doubt related to Yorkshire’s four police forces, who all make use of services provided from a lab in Wakefield through a company called LGC.
LGC outsourced toxicology work for the Yorkshire forces, as well as those in Cleveland, Durham and Northumbria, to Randox as part of their contract to provide services.
At that stage, North Yorkshire had the highest number of cases under review with 63, followed by South Yorkshire with 59, West Yorkshire with 56 and Humberside with 23. Those cases largely related to drug-driving offences.
In May, the NPCC revealed further investigations showed 6,000 toxicology samples, including for murder offences, were in doubt. Officials in Yorkshire said at that stage they were assessing the local impact.
Two men have been arrested and five interviewed under caution by Greater Manchester Police over the alleged manipulation by individuals working at a Randox Testing Services site in Manchester.
The alleged manipulation emerged earlier this year when a data anomaly in a drug driving case was reported to Randox.
The NPCC said retesting was either complete or under way for around 70 per cent of the highest priority cases, with the rest expected to be completed by mid-2018.
Of the around 50 cases due to go to trial which have been dropped, some were discontinued due to there being no sample available for retesting, the sample was insufficient in quality or quantity to allow retesting or there had been degradation of evidence, James Vaughan of the National Police Chiefs' Council said.
Not every court was sympathetic to requests for proceedings to be adjourned, leading to further cases to be ditched, he said.
He added that, to his knowledge, nobody had been held in custody as all the offences were summary.