Spirit of old duke regularly seen in V&A (5)
I believe the answer is:
vodka
'spirit' is the definition.
(I've seen this before)
'old duke regularly seen in va' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'seen in' indicates putting letters inside.
The alternate letters of 'duke' are 'dk'.
'o'+'dk'='odk'
'odk' placed into 'va' is 'VODKA'.
'of' acts as a link.
(Other definitions for vodka that I've seen before include "Colourless liquor" , "Alcoholic spirit of Russian origin" , "Colourless alcoholic spirit associated with Russia" , "Russian alcoholic drink" , "Distilled spirit" .)