Virgin Trains' pie not a crumble (8)
I believe the answer is:
Here is my best explanation:
'virgin' is the definition.
'trains' pie not a crumble' is the subsidiary indication.
'not' indicates named letters should be taken away.
'crumble' indicates an anagram.
'trainspie' with 'a' taken out is 'trinspie'.
'trinspie' with letters rearranged gives 'pristine'.
(Other definitions for pristine that I've seen before include "not spoiled", "ancient", "maiden voyage?", "Immaculate", "Spotless", "Virgin", "Completely free of dirt", "Immaculately clean, unused or untouched", "Pint, sire? (anag)" and "Pure - tire spin (anag)".)