Reports emerged this week that a private health company which analyses forensic samples on behalf of police forces across the UK was embroiled in a scandal over the accuracy of its drug-driving tests.

Two employees of contractor ‘Randox’ have been arrested on suspicion of ‘perverting the course of justice’ as part of ongoing investigations into allegations that samples in hundreds of cases were doctored.

Paul Loughlin, a motoring law specialist and solicitor at the national law firm, Stephensons, said: “With an investigation ongoing, the extent to which results have been misrepresented – and the number of drug-driving cases affected – is still unclear.

“However, reports suggest that the police are already contacting individuals whose cases might have been affected and estimates indicate that hundreds of people could have been convicted on the basis of ‘unsafe’ evidence. If true, this would present a considerable miscarriage of justice – certainly in terms of motoring law.

“If someone has reason to believe that their conviction was based upon flawed or fabricated evidence the first thing they should do is seek professional legal advice. From there, a solicitor will be able to advise the appellant of their options and prospects for success.

“For the most part, the legal system is well equipped to identify and remedy any miscarriages of justice, though what form this will take depends on the time between the initial conviction and the time when new evidence – or doubts about existing evidence – comes to light.

“The window for appeal is 21 days in cases handled by the magistrate’s court and 28 days for cases handled by the Crown Court. The magistrate’s court can also be asked to ‘set aside’ the conviction and reopen the case within 28 days, or later, in exceptional circumstances. However this can only be achieved if the court believes it is in the interest of justice to do so, and the onus is on the appellant to convey the significance of any new evidence. Anecdotal evidence or hearsay would not be sufficient and securing new information can be a costly and time consuming process. In some cases the Criminal Cases Review Commission may need to become involved.

“If a conviction is successfully overturned, then an application can be made for compensation. This is decided by the Justice Secretary. However, those convicted of driving offences – including drug-driving – should not expect any significant sum. The £1 million cap upper limit is usually reserved for those who have spent ten years or more in prison.

“Those wrongly convicted of drug-driving might reasonably expect compensation for things like increased insurance premiums or any financial penalty which was levied. Each case would be considered on its own merits, so there is no automatic right to compensation.”