2. Cockney rhyming slang for 'Slash', meaning to urinate.
3. A slang term for 'Gash' referring to the female genitalia. Although in this case, it is used to refer to any type of sexual contact with a partner, not just 'Gash'
2: I can't hold it any more, I'm going for a Pie and Mash.
Guy: I went and saw my girlfriend last night.
Friend: Sweet, did you get any pie and mash?
Historically, the pies were made from scraps of beef and vegetables, leftovers or from the local markets, under a pastry crust. The mashed potatoes were liberally covered in parsley gravy or "liquor". There has been a great revival in these dishes and quite a number of Pie ‘n’ Mash restaurants can now be found across London.