British trapped in a lounge on fire (6)
I believe the answer is:
ablaze
'on fire' is the definition.
('ablaze' can be a synonym of 'on fire')
'british trapped in a lounge' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'trapped in' indicates putting letters inside.
'lounge' becomes 'laze' (I've seen this before).
'a'+'laze'='alaze'
'b' inserted into 'alaze' is 'ABLAZE'.
(Other definitions for ablaze that I've seen before include "filled with anger" , "Well-lit" , "Fiery" , "On fire, burning" , "Flaming; on fire" .)