The failure by police officers and prosecutors to hand over crucial evidence is the number one cause of unsafe convictions, experts warned last night.

Richard Foster, chairman of the Criminal Cases Review Commission, told The Mail on Sunday that non-disclosure of material that could prove a suspect's innocence is the 'biggest single problem' affecting the right to a fair trial.

He said an 'explosion' of emails, text messages, social media posts and CCTV footage has made the work far harder for detectives, while police budgets have shrunk.

But Mr Foster claimed the difficulty of the task was 'no excuse', and failure to do it right was 'a failure to uphold the rule of law'.

Richard Foster, chairman of the Criminal Cases Review Commission, said an 'explosion' of emails, text messages, social media posts and CCTV footage has made the work far harder for detectives, while police budgets have shrunk

His comments come after a week in which five shocking cases of non-disclosure have come to light.

The rape trial of student Liam Allan was halted only when prosecutors uncovered a disk containing 40,000 messages that showed his accuser had pestered him for casual sex.

Scotland Yard also announced it was reviewing all ongoing rape cases after the collapse of a second sex trial, that of Isaac Itiary, over disclosure problems.

MP's aide Samuel Armstrong was cleared of rape by a jury but said he could have been convicted if his defence team had not obtained crucial phone and medical records days before his trial.

But Mr Foster claimed the difficulty of the task was 'no excuse', and failure to do it right was 'a failure to uphold the rule of law'

Judges also quashed the rape conviction of Danny Kay, who had served two years behind bars, after it emerged that the complainant had deleted Facebook messages showing their sex had been consensual.

And the CCRC itself referred to the Court of Appeal the case of a man jailed for sex with an underage girl in 2007, after its investigators found 'a body of relevant information had not been disclosed to the defence'.

Mr Foster, a former chief executive of the Crown Prosecution Service, said: 'Disclosure is hard work. It can be dull.

It means sifting through huge volumes of material, made more voluminous by the explosion in digital communications and CCTV surveillance. But the fact that the task is harder – and money shorter – is no excuse, especially in serious prosecutions.

'We are talking about whether evidence in our possession justifies us in even bringing a prosecution, let alone convicting someone.'

In a recent speech on fair trials, Mr Foster added: 'Accusers and accused can be put through the mill unnecessarily. At worst, the innocent are wrongly convicted.

'Deliberate non-disclosure should be unthinkable. So why is it the biggest cause of unsafe convictions my commission sees?'