A British journalist is lying (4)
I believe the answer is:
abed
'is lying' is the definition.
(lying abed or in bed)
'a british journalist' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'journalist' becomes 'ed' (short for editor).
'a'+'b'+'ed'='ABED'
(Other definitions for abed that I've seen before include "at rest" , "given blanket coverage?" , "laid up" , "in a comfortable position" , "Sleeping (archaic)" .)