Pub importing old ale ultimately as a unit (2,3)
I believe the answer is:
in one
'as a unit' is the definition.
'pub importing old ale ultimately' is the wordplay.
'pub' becomes 'inn' (I've seen this before).
'importing' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ultimately' says to take the final letters.
The last letter of 'ale' is 'e'.
'inn' placed around 'o' is 'inon'.
'inon'+'e'='IN ONE'
(Other definitions for in one that I've seen before include "united" , "As a single unit" , "Combined" , "A hole . . . . . is a singular golf score" .)