Member initially gets in two beers - barman here one of the best (5,5)
I believe the answer is:
legal eagle
'barman here one of the best' is the definition.
(person from the bar in legal sense)
'member initially gets in two beers' is the wordplay.
'two beers' means two substitutions for 'beer'.
'member' becomes 'leg' (member can mean a limb).
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'beer' becomes 'ale' (type of beer).
'beer' becomes 'ale' (type of beer).
The first letter of 'gets' is 'g'.
'ale'+'ale'='aleale'
'g' put inside 'aleale' is 'aleagle'.
'leg'+'aleagle'='LEGAL EAGLE'
(Other definitions for legal eagle that I've seen before include "Bright lawyer (colloq.)" , "Brief" , "Astute lawyer" , "perhaps the best defence" .)