British equipment in jail (4)
I believe the answer is:
brig
'jail' is the definition.
(I've seen this in another clue)
'british equipment' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'equipment' becomes 'rig' (rig is a kind of equipment).
'b'+'rig'='BRIG'
'in' acts as a link.
(Other definitions for brig that I've seen before include "Two-masted square-rigged vessel" , "'Two-masted,square-rigged ship (4)'" , "A ship; army officer (abbr.)" , "Sailing-vessel" , "Two-masted square-rigger" .)