Wanted gentleman to interrupt activity (7)
I believe the answer is:
desired
'wanted' is the definition.
('desired' can be similar in meaning to 'wanted')
'gentleman to interrupt activity' is the wordplay.
'gentleman' becomes 'sir' (I've seen this before).
'to interrupt' means one lot of letters goes inside another.
'activity' becomes 'deed' (I've seen this in other clues).
'sir' going inside 'deed' is 'DESIRED'.
(Other definitions for desired that I've seen before include "much wished for" , "Lusted-after" , "Had aspired to" , "Sought after" , "requested" .)