Casual drink in Spain that is welcomed by both sides (8)
I believe the answer is:
cavalier
'casual' is the definition.
(I've seen this before)
'drink in spain that is welcomed by both sides' is the wordplay.
'drink in spain' becomes 'cava' (Spanish drink).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'welcomed by' indicates putting letters inside (letters welcomed inside).
'both sides' becomes 'LR' (abbreviation for left and right).
'ie' going into 'lr' is 'lier'.
'cava'+'lier'='CAVALIER'
(Other definitions for cavalier that I've seen before include "Incautious" , "Civil War participant" , "oblivious to consequences" , "Offhand - Charles I supporter" , "Arbitrary, off-hand" .)