A Liberal supporting taxi group (5)
I believe the answer is:
cabal
'group' is the definition.
'a liberal supporting taxi' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'taxi' becomes 'cab' (synonyms).
'a'+'l'='al'
'al' put after 'cab' is 'CABAL'.
(Other definitions for cabal that I've seen before include "Group in plot" , "Small group involved with intrigue" , "Group of political intriguers" , "Plotting group" , "Secret political group" .)