Drive out the Spanish supporting former power (5)
I believe the answer is:
expel
'drive out' is the definition.
(I've seen this before)
'the spanish supporting former power' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'former' becomes 'ex' (prefix meaning former or onetime).
'power' becomes 'p' (symbol in physics).
'ex'+'p'='exp'
'el' after 'exp' is 'EXPEL'.
(Other definitions for expel that I've seen before include "Put out" , "Eject (from school)" , "Deport" , "Banish (undesirable alien?)" , "Get rid" .)