RANDOX Testing Services (RTS) are being investigated after two of its employees were arrested over allegations that hundreds of cases handled by the company were affected by "data manipulation".
The firm, which is based in Northern Ireland with offices in London and Manchester, is used by police forces across the UK to analyse samples used in prosecutions.
Two men were arrested by Greater Manchester Police (GMP) over allegations that some 484 cases handled by RTS were affected by what the National Police Chiefs' Council (NPCC) called "data manipulation".
The allegations relate to drug tests analysed at its Manchester office. The men, aged 47 and 31, were arrested on suspicion of perverting the course of justice and bailed.
But it raised the prospect that hundreds of people could have been the victims of miscarriages of justice because of convictions based on incorrect test results in their cases.
In a statement, RTS said the investigation centres on the "manipulation of quality control data, which supports test results".
"A number of toxicology results have been compromised," it said.
"RTS are working tirelessly to fully assess the impact and implications for each case. Where possible, when viable, samples will be re-run to provide robust, uncompromised results.
"There is no question mark over the RTS quality system or the robustness of our practices and procedures."
It said the issue "came to light as a result of an internal investigation" and the probe was limited to its Manchester site and two men who worked there for three years.
Chief Constable Debbie Simpson, the National Police Chiefs' Council lead for forensic science, said Randox had provided each force with a list of cases that could have been affected.
