Thousands of criminal investigations are being re-examined after suspicions that lab staff tampered with forensic tests.

They could include murder and rape cases where defendants were convicted on evidence involving drug analysis.

Some 6,000 blood samples are being retested after two scientists working for Randox Testing Services since 2014 were arrested for "manipulating data".

Randox is one of six companies licensed to carry out toxicology tests for various police forces in England and Wales.

Dorset's Deputy Chief Constable James Vaughan said: "It is deeply worrying because the integrity of forensic testing is sacrosanct in the criminal justice system.


"The vast majority of these cases involve drug-driving, but there are likely to be more serious cases affected, including murder and rape."

Mr Vaughan said it was unlikely a murder or rape conviction hung on vital toxicology tests, but he could not rule it out.

Image: Several hundred samples have been retested. File pic

So far, several hundred samples have been retested and have produced the same results as they did when first tested, Mr Vaughan said.

He believes scores of cases could be referred to the Appeal Court, and those where key blood samples had been destroyed would almost certainly result in acquittals.

The two suspects have been questioned on suspicion of perverting the course of justice and released on bail until the end of this month.

They worked for two other forensic science companies before Randox, so the investigation could expand.

Some suspects who had been told they faced no further action could end up being prosecuted if the data was altered in their favour.

The conclusions of some inquests could also be quashed.

Dr Mark Piper, head of toxicology at Randox Testing Services, said: "We regret the concerns that these developments will inevitably cause.

"We are taking all possible responsible actions to allay them.

"RTS are closely engaged with all related police forces, and the process of retesting samples at an appropriately accredited external laboratory is underway. RTS will manage this stage and cover all associated testing costs."