From Longman Dictionary of Contemporary Englishhave it off/away with somebodyhave it off/away with somebody British English informal to have sex with someone → have
Examples from the Corpus
have it off/away with somebody• Rush round here every Wednesday afternoon, have it off with Angy and rush back.• Also I don't want him to try to have it off with some one else.• Dave Mellor did not have it away with that repellent tart.• Was I going to have it off with this woman and a couple of goats? 