Demonstrate in favour of group returning to Thailand (7)
I believe the answer is:
protest
'demonstrate' is the definition.
(I've seen this before)
'in favour of group returning to thailand' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'group' becomes 'set'.
'returning' is a reversal indicator.
'to thailand' becomes 't' (abbreviation on car registration plates).
'set' reversed gives 'tes'.
'pro'+'tes'+'t'='PROTEST'
(Other definitions for protest that I've seen before include "Object loudly" , "Demurral" , "Complaint" , "Potters (anag.)" , "Spotter of objection" .)