The Metropolitan Police is launching a review of all ongoing sex crime investigations, after the collapse of two rape cases in a week.
On Tuesday, prosecutors dropped a case against Isaac Itiary, who had been charged with raping a child under 16.
The defendant was charged in July, but "relevant" evidence was only provided by police in recent days.
Last week, the trial of Liam Allan collapsed because of the late disclosure of evidence by the Met.
In the case of Isaac Itiary, the Crown Prosecution Service said the new material provided by Scotland Yard meant the case could not proceed.
A spokesman said: "On 17 December, the police provided new material to the CPS, which had previously been requested, and this was reviewed.
"Prosecutors decided that there was no longer a realistic prospect of conviction and we offered no evidence against the defendant at a hearing today."
The review is intended to ensure that all digital evidence in other sex crime cases has been disclosed to the CPS.
Liam Allan was charged with 12 counts of rape and sexual assault but his trial collapsed after police were ordered to hand over phone records.
A computer disk containing 40,000 messages revealed that the alleged victim had pestered him for "casual sex".
The 22-year-old student, who spent almost two years on bail, has said he intends to sue the Met.
Commander Richard Smith, who oversees the Met's rape investigations, said he understood that the failure of the latest case would raise further concerns.
He added: "The Met is completely committed to understanding what went wrong in the case of Mr Allan and is carrying out a joint review with the CPS, the findings of which will be published."