Re: Police in impossible position
It's true that consent can be withdrawn. If the complainant says "I agreed but then changed my mind", then before-the-event phone evidence is probably not relevant.
But if the complainant says in an interview "I never agreed to sex", then there is evidence found that they DID agree to meet up for sex, then you just caught the complainant in a lie and that would discredit their statement. If there's no other evidence, that would cause the case to collapse.