Murder and rape offences are among 80 cases in Norfolk and Suffolk where convictions could be jeopardised due to suspected manipulation of forensic evidence.

Norfolk has 52 cases being scrutinised in the current inquiry relating to Randox Testing Services in Manchester, while Suffolk has 28, police have said.

The Crown Prosecution Service and the Forensic Science Regulator now fear more than 6,000 toxicology samples nationally could have been manipulated.

This could potentially lead to miscarriages of justice in hundreds of cases.

Two men – aged 31 and 47 - at the Manchester laboratory were arrested on suspicion of perverting the course of justice in February after concerns forensic tests had been tampered with.

The National Police Chiefs' Council said while the majority of cases affected were traffic offences, other convictions – including murder and rape cases, where defendants were found guilty on evidence involving drug analysis – could be overturned.

It is understood Norfolk and Suffolk Police are still waiting to learn the significance of this, but no formal appeals against convictions have been lodged.

Detective Chief Superintendent David Skevington said: 'Suffolk and Norfolk were originally notified of eight cases which were affected by the issues involving sub-contraction of toxicology testing to Randox Testing Services, with more recent events increasing this number to 80.

'This includes 52 in Norfolk and 28 in Suffolk, with investigations ranging from murder to rape and drug-driving offences.

'The manipulation of forensics the national inquiry has uncovered has resulted in an extremely serious impact on the criminal justice system.

'Both forces are doing everything they can, as quickly as they can, to identify cases where there could have been miscarriages of justice as a result.

'The constabularies are prioritising the most serious and pressing cases but all cases where there could have been an impact on prosecution will be assessed, retested and appropriate action taken.

'Police and the CPS will make contact with any affected members of the public in due course.'

In February Randox Testing Services, which is part of the Northern Ireland-based Randox Laboratories group, said it was treating the matter with the 'utmost seriousness'.

The laboratory is used by police forces across the UK to analyse samples used in prosecutions.

At the time, police chiefs said 484 cases handled by the firm since November 2015 could be affected.

But investigators are now looking into alleged manipulation of data from toxicology testing carried out by the company from 2014.

According to reports, initial retesting of samples still held has shown broadly the same results as presented in court cases.

But it is understood that 10pc of samples are no longer held and cannot be retested, and therefore can no longer be relied on.

Experts say much could depend on how crucial the toxicology test results were in the prosecution case.

And while it is unlikely that the outcome of a murder case would hinge on a drug test, it could have an impact on rape cases if drugs were suspected to be involved.

The Guardian reported that some sources believed a small number of serious cases may end up being referred to the court of appeal.

But these would be cases where the original sample tests cannot be found and retested.

The alleged manipulation relates to data describing the findings of the test samples, as opposed to the interfering with the samples themselves, police said.

Some cases have been adjourned while samples are reexamined, and priority is being given to cases that are about to come to court.

Randox said its accreditation for liquid chromatography mass-spectrometry testing, a common method used in drug toxicology testing, had been suspended at its laboratory in Manchester and in Crumlin, Northern Ireland.

A spokesman 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.'