Detective left clairvoyant nursing national beer (8)
I believe the answer is:
pilsener
'beer' is the definition.
(pilsener is a kind of beer)
'detective left clairvoyant nursing national' is the wordplay.
'detective' becomes 'pi' (private eye).
'left' becomes 'l' (common abbreviation).
'clairvoyant' becomes 'seer' (I've seen this in another clue).
'nursing' means one lot of letters goes inside another.
'national' becomes 'n' (abbreviation listed in Chambers).
'seer' enclosing 'n' is 'sener'.
'pi'+'l'+'sener'='PILSENER'
(Other definitions for pilsener that I've seen before include "Beer" , "Lager named after the town of its origin now in the Czech Republic" , "Kind of lager" .)