A bloomer taking part in such a rebellion (8)
I believe the answer is:
harebell
'a bloomer' is the definition.
(I've seen this before)
'part in such a rebellion' is the wordplay.
'part in' says the answer is hidden in the clue.
'HAREBELL' can be found hidden inside 'such a rebellion'.
'taking' acts as a link.
(Other definitions for harebell that I've seen before include "Blue wild flower -- beer hall (anag)" , "Delicate blue campanula" , "One to blossom" , "Plant" , "Pale blue flower in beer hall, oddly" .)