Around 50 suspected drug drivers have walked free after police admitted 10,000 forensic blood samples may have been manipulated by rogue scientists.

The motorists had been arrested on suspicion of driving under the influence of drugs, including mind altering Class A narcotics, such as cocaine and ecstasy.

The prosecutions hinged on blood samples taken from the suspects which would have shown the amount of drugs in the system.

But the cases had to be thrown out after it emerged that the samples were among thousands that could have been manipulated by a massive breach at a forensics laboratory in Manchester.

In addition two cases involving motorists convicted of causing deaths while drug driving have been referred to the Court of Appeal.

When the breach was discovered earlier this year, the National Police Chiefs' Council (NPCC) said it feared almost 500 criminal cases could be affected.

But they have now conceded the figure was nearer 10,000, including 1,000 sex offences, 275 murders and 700 offences involving violence.

Two former workers at the Randox Testing Services (RTS) laboratory in Manchester have been arrested and five others questioned under caution in connection with the alleged tampering.

Forensic scientists are currently working around the clock to re-test all the affected samples, but it could be many months before all the work has been completed.