THE deputy chief constable of Dorset Police has spoke of his “grave concerns” after 10,000 potential cases of data manipulation were identified at a forensics lab.

Scores of prosecutions around the country have been dropped and several convictions now hang in the balance.

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.

Dorset Police has identified 384 affected cases.

Three-quarters of the cases nationally were traffic offences such as drug driving - with the rest including violent crime, sexual offences and unexplained deaths, spanning back to 2013.

Toxicology tests are carried out to detect the presence of drugs or alcohol in someone's hair, blood or urine and can be relied upon as evidence in court.

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, violence or murder, the NPCC said.

Two men have been arrested and five interviewed by police over the alleged manipulation by individuals working at a Randox Testing Services (RTS) site in Manchester.

Speaking in his role as the NPCC forensic expert, deputy chief constable James Vaughan 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.”

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

The NPCC revealed retesting was either complete or under way for around 70 per cent of the 900 highest priority cases, with the rest expected to be completed by mid-2018.

These include live investigations approaching or in trial, those convicted but not sentenced, those bailed in advance of trial or sentence and convictions where the defendant is in prison.

Dorset Police identified 384 cases potentially affected.

Of these, 25 are Priority One cases, the force said, with 243 at Priority Three and 116 at Priority Four.

268 cases require a re-rest, of which 86 have already been sent for re-testing.

Some 49 re-tests have already been completed, including all Priority One cases. Of these, 25 samples matched the original test result. The force said that degradation of the original sample may explain why the other 24 cases did not match the original sample.