Squeezing party into lobby (8,5)
I believe the answer is:
pressure group
'lobby' is the definition.
(I know that lobby can be written as pressure group)
'squeezing party' is the wordplay.
'squeezing' becomes 'pressure' (I've seen this in another clue).
'party' becomes 'group' (group of people).
'pressure'+'group'='PRESSURE GROUP'
'into' is the link.
(Other definitions for pressure group that I've seen before include "People promoting a particular view" , "Policy promoters" , "Lobbying body" , "People aiming to influence public policy" , "Lobby" .)