Don't laugh, if it was here, then if he ended up being found not guilty through the victim not providing evidence or faltering under questioning he could most likely then claim for damages under crimes compensation as she did not advise him that she was positive before hand.
As screwed up as that sounds if it was consensual and she didn't tell him then she would be committing the crime and so he's entitled to damages so if he's not guilty then she may be liable.

