Was jumper found in H&M loo? (8)
I believe the answer is:
washroom
'loo?' is the definition.
(thesaurus)
'was jumper found in hm' is the wordplay.
'jumper' becomes 'roo' (I've seen this before).
'found in' means one lot of letters goes inside another.
'roo' put within 'hm' is 'hroom'.
'was'+'hroom'='WASHROOM'
(Other definitions for washroom that I've seen before include "Where Americans go" , "Clean up place" , "bog across the pond" , "US loo" .)