Spirit bottle regularly found in enclosure (6)
I believe the answer is:
poteen
'spirit' is the definition.
(I've seen this before)
'bottle regularly found in enclosure' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'found in' means one lot of letters goes inside another.
'enclosure' becomes 'pen' (pen is a kind of enclosure).
The alternating letters of 'bottle' are 'ote'.
'ote' placed into 'pen' is 'POTEEN'.
(Other definitions for poteen that I've seen before include "Home made spirit" , "illicit booze" , "Illegal drink" , "Illicit Irish hooch" , "Unlawfully distilled Irish whiskey" .)