Joely Richardson's helping London theatre (5)
I believe the answer is:
lyric
'london theatre' is the definition.
(the Lyric is a West End theatre)
'joely richardson's helping' is the wordplay.
'helping' says the answer is hidden in the clue (a helping or portion of the letters).
'LYRIC' is hidden within 'joely richardsons'.
(Other definitions for lyric that I've seen before include "something to sing about? On the contrary" , "Expressing personal feelings" , "Cyril (anag.)" , "Melodic" , "(Of poetry) expressing emotion" .)