Porter perhaps is blocking that gangway (5)
I believe the answer is:
aisle
'gangway' is the definition.
('aisle' can be a synonym of 'gangway')
'porter perhaps is blocking' is the wordplay.
'porter perhaps' becomes 'ale' (porter is a kind of ale).
'blocking' indicates putting letters inside.
'ale' going around 'is' is 'AISLE'.
'that' is the link.
(Other definitions for aisle that I've seen before include "Passageway between pews" , "Passage between seating blocks" , "The way to get married in church?" , "way to the altar?" , "Supermarket feature" .)