Briton back on his bed (4)
I believe the answer is:
scot
'briton' is the definition.
(Scot is a type of Briton)
'back on his bed' is the wordplay.
'back on' says to take the final letters (the letter at the back).
'bed' becomes 'cot' (cot is a kind of bed).
The last letter of 'his' is 's'.
's'+'cot'='SCOT'
(Other definitions for scot that I've seen before include "Burns for one" , "levy, once" , "Stevenson was one" , "Northern member of UK" , "Someone from Dundee?" .)