R v K

 A man had sex with a 14 year old girl, genuinely, though not reasonably, believing that she was 14. HL quashed conviction, saying that the belief as to the victim’s age had merely to be genuine and honest. However, as Lord Bingham said, the unreasonableness of the belief is not irrelevant, since a very far fetched claim as to what D believe might make the jury less wiling to accept that he actually believed it.