London medical schools don't recognise others as valid institutions and regard anyone who trained anywhere other than their home school as an incompetent charlatan and fraud. At least in the Union culture and songs.
In reality, there's a good deal of respect between the schools, a fair amount of joint clubs (Joint newspaper, United Hospitals sports teams, ULU etc), people moving between schools through their careers in jobs and intercalations and stuff and people placed at the same district general hospitals. That and a great deal of piss-taking, which is mixed in intent and taste. Probably one of those things to be played as quietly as possible until you know the rules and the people you're speaking to really.