Gay musical in which George Best playing with a harp (3,7,5)
I believe the answer is:
the beggars opera
'gay musical' is the definition.
(I've seen this before)
'george best playing with a harp' is the wordplay.
'playing with' is an anagram indicator.
'george'+'best'='georgebest'
'a'+'harp'='aharp'
'georgebest' mixed up with 'aharp' makes 'THE BEGGARS OPERA'.
'in which' acts as a link.
(Other definitions for the beggars opera that I've seen before include "Gay musical" , "Gay entertainment" , "Gay work" .)