The collapse of two cases in a week has prompted London's Metropolitan Police force to urgently review all its current rape investigations.
The prosecutions were stopped because officers had not provided vital evidence to the defence.
There are now fears more cases could be thrown out and warnings that officers are making basic errors.
Isaac Itiary, 25, had been awaiting trial for six counts of sexual activity with a child and two counts of rape.
But the charges against him were dropped suddenly yesterday when police revealed there were text messages that showed the girl at the centre of the allegations had posed as a 19-year-old.
Just days earlier, another man, 22 year-old Liam Allan, had his case thrown out because officers had not handed over around 40,000 text messages — some of which cleared his name.
"The last 10 years I've just spent worrying and not really concentrating on anything," Mr Allan said.
"So it has completely ripped apart my normal sort of personal life."
Mr Allan has threatened to sue police and prosecutors, accusing them of chasing convictions as though they were sales targets.
Police are now carrying out a review, with prosecutors to work out exactly what went wrong in Mr Allan's case, and why the information was not handed over sooner.
Commander Richard Smith said officers were also examining all the evidence they have in all of their current sex offence cases.
"Our priority is those 30-something [cases] where trials are about to start," Mr Smith said.
"I have no reason to believe that there are any problems with any of those cases, it is a pragmatic step to conduct that check now."
'Broader review, not internal, required'
In the past police often faced complaints they were not treating sexual assault complaints seriously enough.
Now there are claims the accused are not being treated fairly.
Lord Paddick, a former deputy assistant commissioner, said a broader review was required.
"The real issue here is giving the public confidence in the criminal justice system," he said.
"I don't see how an internal review by the police and the Crown prosecution service can give the public that confidence.
"Particularly if there's been a change in culture swinging against believing people who come up with a reasonable explanation for their behaviour."
Conviction rates in reported rape cases are low and a study from the UK home office suggested only about 4 per cent of reported sexual violence cases were false.
But UK Prime Minister Theresa May told Parliament overnight she wanted to make sure police were always disclosing all available evidence.
"I think it is important that we look at this again to make sure that we are truly providing justice," she said.
