Claim Tommy is occasionally permitted each drink (8,3)
I believe the answer is:
camomile tea
'drink' is the definition.
(camomile tea is a kind of drink)
'claim tommy is occasionally permitted each' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'permitted' becomes 'let' (to let something happen is to permit it).
'each' becomes 'ea' (abbreviation).
'claim'+'tommy'+'is'='claimtommyis'
The alternating letters of 'claimtommyis' are 'camomi'.
'camomi'+'let'+'ea'='CAMOMILE TEA'
(Other definitions for camomile tea that I've seen before include "Herbal drink" , "Herbal 50 ac" .)