Almost 500 drug-drive prosecutions are to be re-investigated after fears test data may have been manipulated.

Bosses at Randox Testing Services believe there are as many as 484 suspected cases of manipulation at its Manchester office.

The company has provided forensic services to police forces, including Greater Manchester Police , for the past two years.

Police have launched a probe to find out if lab workers at the health company doctored the results of tests on blood, urine and hair.

Two analysts have been questioned over alleged tampering at a lab used by more than half of UK police forces. They are now on police bail.

One has been suspended from the lab, the M.E.N understands.

Scores of court cases will now need to be reviewed by the Crown Prosecution Service to see if they were affected by “compromised data”.

A CPS spokesperson said: “We are working with the Home Office, police and the Office of the Forensic Science Regulator to assess the impact of the testing failure at Randox Testing Services.

“This includes establishing which cases have been affected by this issue and working with other agencies to decide what action should be taken in relation to those cases.”

Police forces have been provided with a list cases that may have been effected.

Convictions could be quashed if the evidence is found to be false, the M.E.N understands.

Chf Con Debbie Simpson, of the National Police Chiefs Council, said: “We have been made aware of a quality failure with Randox Testing Services which is currently being investigated and a criminal inquiry has been launched by Greater Manchester Police.

(Image: PA)

“Randox has provided each force with a list of cases that could have been effected. Working in partnership with the Crown Prosecution Service, we have provided guidance to forces so they are able to review each case to determine if compromised data played a part in prosecution and the CPS will then take appropriate action in any cases identified.

“While this investigation is ongoing, we are working with a number of forensic service providers and the Forensic Science Regulator to ensure that any requirement for forensic services is dealt with in the normal timeframes.”

It is believed that the investigation could spark a flood of compensation claims.

The majority of samples are linked to criminal investigations. Most relate to drug-driving but a small proportion of tests were carried out on samples from suspected victims of crime.

Randox alerted authorities after an internal probe last month found evidence to suggest “toxicology data was compromised”.

It added: “We take this alleged breach of our stringent quality assurance systems very seriously.”

The company's quality control procedures found data anomolies.

The Home Secretary has also been made aware of the investigation.

The Home Office said: “The matter is being urgently investigated by the Forensic Science Regulator and UK Accreditation Service.”

A Greater Manchester Police spokesperson said the force has been asked to conduct a criminal investigation into forensic results issued by Randox Testing Services.

They added: “Randox Testing Services have provided forensic services to police forces, including GMP, for the past two years.

“The organisation is being fully co-operative of the investigation.

“Two men, a 47 year-old and a 31 year-old, have been arrested on suspicion of perverting the course of justice and released on bail until 6 March 2017 pending further enquiries.”