Oxford college's rustic porch is vandalised (6,7)
I believe the answer is:
corpus christi
'oxford college's' is the definition.
(I've seen this before)
'rustic porch is vandalised' is the wordplay.
'vandalised' is an anagram indicator.
'rustic'+'porch'+'is'='rusticporchis'
'rusticporchis' is an anagram of 'CORPUS CHRISTI'.
(Other definitions for corpus christi that I've seen before include "Texan city: name shared by colleges at Oxford and Cambridge" , "Oxbridge college" , "Oxford or Cambridge college" , "Church festival; Oxford college" .)