Returning United Kingdom party's prestige (5)
I believe the answer is:
kudos
'prestige' is the definition.
(I've seen this before)
'returning united kingdom party's' is the wordplay.
'returning' shows that the letters should be reversed in order.
'united kingdom' becomes 'UK' (synonyms).
'party's' becomes 'do's' (do is a kind of party).
'uk' back-to-front is 'ku'.
'ku'+'dos'='KUDOS'
(Other definitions for kudos that I've seen before include "Pat on the back" , "Informal honour of glory" , "Praise and honours" , "Fame - prestige" , "Praise, honour" .)