In bar seats perhaps but they won't be drinking (10)
I believe the answer is:
abstainers
'they won't be drinking' is the definition.
(I've seen this before)
'in bar seats perhaps' is the wordplay.
'perhaps' indicates an anagram.
'in'+'bar'+'seats'='inbarseats'
'inbarseats' with letters rearranged gives 'ABSTAINERS'.
'but' acts as a link.
(Other definitions for abstainers that I've seen before include "They won't be drinking" , "Avoiders of alcohol" .)