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Labour has blamed austerity in the criminal justice system for the recent collapse of two rape cases amid concerns about the disclosure of evidence.

Shadow attorney general Baroness Chakrabarti said the increasing prevalence of social media and text messaging has made the handing over of evidence to lawyers an increasingly "labour-intensive" process.

Metropolitan Police Commissioner Cressida Dick has said disclosure of evidence is becoming "increasingly incredibly complex and demanding" in the digital age.

Scotland Yard is urgently reviewing around 30 sex cases due to go to court after the rape trial of Liam Allan was halted last week and the prosecution of Isaac Itiary, accused of raping a child, collapsed on Tuesday.

On Thursday, Samuel Armstrong, chief of staff to Conservative MP Craig Mackinlay, claimed he was cleared of raping a woman in his boss's office after "crucial evidence" was disclosed just days before his trial.

Lady Chakrabarti called for the police and Crown Prosecution Service (CPS) to be properly trained and resourced, and sufficient legal aid to be made available for defence teams to bring challenges when they receive evidence.

She told BBC Radio 4's Today programme: "I have been hearing as have others on an increasing basis about a system that is under-funded.

"And under-funding in relation to disclosure in particular, which these days with social media and text messaging and so on can be a really labour-intensive process."

She added: "It's not happened in these two rape cases until late in the day, is the concern, but of course if we've got a problem with disclosure in this country it won't just be about sex cases, it could potentially be about all sorts of very serious cases, and we cannot have an undermining of confidence, whether on the part of complainants or of defendants in something as serious as the criminal justice system."

Last week the trial of Mr Allan, 22, was halted at Croydon Crown Court as it was decided there was "no longer a realistic prospect of conviction".

Police are understood to have looked at thousands of phone messages when reviewing evidence, but it was not until the prosecution was close to trial that Met officers disclosed messages between the complainant and her friends which cast doubt on the case against Mr Allan.

The CPS offered no evidence against Mr Itiary, who was facing trial at Inner London Crown Court charged with the rape of a child under 16, along with other offences.

He was charged in July, but police only disclosed further "relevant material" in response to the defence case statement submitted on December 15.

Mr Armstrong, 24, was accused of attacking the young parliamentary worker when she fell asleep after a night drinking in the Houses of Parliament.

On Thursday, he wiped tears from his eyes after a jury of seven women and five men found him not guilty of two counts of rape, one of sexual assault and one of assault by penetration, after a two-week trial at Southwark Crown Court.

Mr Armstrong and his lawyers refused to elaborate on what evidence he was referring to, but the court heard the complainant initially refused to give police access to her mobile phone and medical records.

In messages recovered from her phone, she said she had contacted a journalist just hours after the alleged attack to secure a "sympathetic" write-up, while her medical notes revealed details of a history of mental health issues, including depression and anxiety.

Additional reporting by Press Association.