Mobile evidence has been used in celebrity sex trials, such as that of ex Sunderland footballer Cabral, who was cleared of raping a woman he met in a nightclub yesterday

Court officials have warned that the number of sex offence cases at crown courts is putting a strain on the criminal justice system, after it was revealed that they account for 50% of cases heard.

And mobile technology is partly to blame - with so many cases now requiring digital evidence from phones and social media, which can take weeks to acquire and process.

Courts have had to take urgent action, including making judges sit for an extra 7,500 days in total last year to hear the cases, which can often be lengthy and complex.

Trials are routinely delayed by several months, and digital evidence turning up too late can cause them to collapse.

Mobile evidence has been used in celebrity sex trials, such as that of ex Sunderland footballer Cabral, who was cleared of raping a woman he met in a nightclub yesterday.

The jury's verdicts came after mobile phone footage played in court showed the woman in bed with Newcastle players Kevin Mbabu and Rolando Aarons days before the trial began.

There was a 41% rise in the reportage of sexual offences in the 12 months to last December, and judges say that they form the biggest group of crimes nationally.

One told The Times: 'About half of these are allegations of historical sex offences.

'When police arrest any alleged sex offender, they almost invariable seize computers and mobile phones. These are sent to forensic investigators - they are good and thorough but can take months and often over a year before producing any report.'

An Office of National Statistics report last year said the 43 forces in England and Wales recorded 33,431 rapes and 66,178 other sexual offences, a total of 99,609 that was the highest since the National Crime Recording Standard was introduced 13 years ago.

Recorded separately, rape reports rose 39% year-on-year and other sex crimes 35%. The rate of sexual offences has doubled in the past year, from one in every 1,000 people to two in every 1,000.

The ONS said the rise was 'likely to be due to an improvement in recording by the police and an increase in the willingness of victims to come forward and report to the police', with previous recent increases attributed to the profile of the Yewtree paedophile probe.