UK apt to become broken (5)
I believe the answer is:
kaput
'broken' is the definition.
(I've seen this in another clue)
'uk apt to become' is the wordplay.
'to become' indicates anagramming the letters.
'uk'+'apt'='ukapt'
'ukapt' with letters rearranged gives 'KAPUT'.
(Other definitions for kaput that I've seen before include "No longer functioning" , "Broken or finished - in Germany" , "Defunct (informal)" , "Out of order,or broken, from German" , "Ruined (slang)" .)