European spies held in China waste away (8)
I believe the answer is:
emaciate
'waste away' is the definition.
(I've seen this before)
'european spies held in china' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'spies' becomes 'cia'.
'held in' means one lot of letters goes inside another.
'china' becomes 'mate' ('China plate' is rhyming slang for 'mate').
'cia' put inside 'mate' is 'maciate'.
'e'+'maciate'='EMACIATE'
(Other definitions for emaciate that I've seen before include "Waste away" , "Make extremely thin" , "get very thin" .)