An investigation into alleged data manipulation at a forensics laboratory has identified more than 10,000 cases which "may have been affected", the National Police Chiefs' Council has said.
The NPCC said three-quarters of the cases, 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.
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.