Continuity mistake: In the cafe when Gerald says his line "must dash got a deadline to meet on the school magazine" the same girl (with long brown hair) walks behind him twice within a few seconds.
Revealing mistake: Carlene makes Joanna a cup of coffee in the common room after finding her drunk in the toilet. Joanna refuses to drink it and drops the cup, breaking it - it's obvious that there was never any coffee in the cup.