Mind you the writer - Alan Plater - is a serious jazz buff. Check out his Biederbecke series for some great jazz composed for the films by Frank Ricotti and featuring Kenny Baker - check out "Live at the Limping Whippet". He also gave Tubby Hayes his first (only?) part in a BBC play, collaborated a lot with Alan Barnes and was a great supporter (in hard times) of the great Joe Harriott.
Rhys, those keycups are rather distinctive. But I have to confess 'no idea'. Do tell.