In this instance the prosecution offered no evidence and the case was dropped. So yes, theres the presumption of innocence of course, but it's not the same as the headlines declaring that they've been cleared, they've not, because they've not been tried, no evidence was heard and no court decision reached.
My understanding is that if a matter reaches trial and the prosecution offer no evidence the judge can dismiss the case without the need of a jury, and the defendant is formally acquitted. This means that the defendant cannot be retried. It is just the same as a not guilty verdict by a jury.
Surprisingly, The Sun's report has more relevant details than the Gruaniad.
First point: she was alleged victim in a separate rape trial and changed her evidence. Her sexual history isn't relevant. The fact she changed her evidence is: her truthfulness would have been put in issue, weakening the prosecution case.
Second point: the rape was filmed and it was consensual. Filming it might involve an entirely separate crime, but not rape.
Third point, and it's hard to overstate the seriousness of this: the police did not disclose these matters to the defence. Goodness knows how this happened but at best that is negligent and at worst misconduct. Defendants have the right to know all the evidence held by the authorities against them, and that includes rape defendants. If the authorities get slack about this, innocent people go to prison.
I suspect the judge would have handed the prosecution its arse on a platter had it wanted to proceed with the trial.
Scarlet it does not good speculating on why the woman complained to the police. In any event, it is the responsiblity of the CPS together with the police to ensure that poor cases are not taken to court. Clearly this didn't happen here. This, together with the Waterloo sexual assault case (where video evidence was adjusted without the defence being informed) makes me believe that the police / CPS are coming under pressure to prosecute cases that are so weak that the liberty of innocent people is being put at risk.