Virgin Trains' pie not a crumble (8)
I believe the answer is:
pristine
'virgin' is the definition.
(I've seen this before)
'trains' pie not a crumble' is the wordplay.
'not' indicates named letters should be taken away.
'crumble' indicates an anagram.
'trains'+'pie'='trainspie'
'trainspie' with 'a' removed is 'trinspie'.
'trinspie' anagrammed gives 'PRISTINE'.
(Other definitions for pristine that I've seen before include "Immaculate" , "not spoiled" , "Fresh and clean as if new" , "Unchanged or unspoilt" , "Spotless" .)