War memorial discovered by musicians in London with drum entering church (8)
I believe the answer is:
cenotaph
'war memorial' is the definition.
(type of memorial to war dead)
'musicians in london with drum entering church' is the wordplay.
'musicians in london' becomes 'ENO' (English National Opera).
'with' means one lot of letters go next to another.
'drum' becomes 'tap' (both can mean to make a noise by hitting).
'entering' indicates putting letters inside.
'church' becomes 'ch' (common abbreviation).
'eno'+'tap'='enotap'
'enotap' going inside 'ch' is 'CENOTAPH'.
'discovered by' is the link.
(Other definitions for cenotaph that I've seen before include "Monument honouring the fallen" , "Tomb-like monument to people buried elsewhere" , "Empty tomb" , "Monument to the war dead" , "Feature of Whitehall" .)