A Butlins rebuilt in Turkish city (8)
I believe the answer is:
istanbul
'turkish city' is the definition.
(I've seen this before)
'a butlins rebuilt in' is the wordplay.
'rebuilt' indicates anagramming the letters.
'in' indicates putting letters inside.
'butlins' anagrammed gives 'istnbul'.
'a' placed within 'istnbul' is 'ISTANBUL'.
(Other definitions for istanbul that I've seen before include "Turkey's largest city" , "Nail bust in the Turkish city" , "City straddling the Bosporus" , "Take the Latin bus out to Turkey" , "Modern Byzantium" .)