HUNDREDS of prosecutions and convictions in Hampshire hang in the balance after it was revealed that tests undertaken at forensic lab may have been manipulated.

Two men have been arrested and five interviewed under caution by Greater Manchester Police over the alleged manipulation at a Randox Testing Services (RTS) site in Manchester

The alleged misconduct emerged earlier this year when a data anomaly in a drug driving case was reported to RTS.

Hampshire is among the forces which use the lab and 474 cases from the county, the majority of which are driving offences, but include violent and sexual offences, could be affected.

So far 40 forensics samples from the cases have been re-tested. Nine results have shown differences and a further seven are being reviewed to establish if the results are significantly different, the force said.

Across the country scores of prosecutions have been dropped and several convictions hang in the balance after 10,000 potential cases of data manipulation were identified at a forensics lab.

The National Police Chiefs' Council (NPCC) said forensic tests across 42 police forces, including rapes and murders, were being considered possibly unreliable and needed re-examining.

As a result of the breach in standards, around 50 drug driving investigations have been discontinued, while two road death convictions have been referred to the Court of Appeal.

Retests have so far found no impact on cases of sexual offence cases, violence or murder, the NPCC said.

The Forensic Science Regulator said in terms of numbers of cases, it was the biggest issue of its kind ever to happen in the UK.

Deputy Chief Constable James Vaughan, the NPCC forensic expert, said: "This is of grave concern to me, it is of great concern to policing and out partners in criminal justice and we are taking it extremely seriously and provided a nationally co-ordinated and very swift, robust response, to understand more detail.

"Forensic science in criminal justice is paramount and vital to confidence in the criminal justice system."

Potential data manipulation at a separate facility, Trimega Laboratories, is also being investigated by Greater Manchester Police - affecting child protection and family court cases, the NPCC said.

It is understood the two suspects arrested in connection with the alleged malpractice also worked for Trimega.

It is expected the full retesting process will take two to three years.

Gillian Tully, of the Forensic Science Regulator, said: "I'm not going to speculate on any motives because obviously there is an ongoing criminal investigation but we cannot just say it was a minor technical issue."

She added: "In terms of the number of cases affected, it is certainly the biggest thing that I'm aware of to happen in this country."

All major forensic toxicology suppliers had been asked to carry out a detailed audit of a sample of their cases to ensure the issue was not more widespread.The audits uncovered no such data manipulation.