Supporter of revolutionary ruler imprisoning Her Majesty (11)
I believe the answer is:
cheerleader
'supporter' is the definition.
'revolutionary ruler imprisoning her majesty' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'ruler' becomes 'leader' (I've seen this before**).
'imprisoning' is an insertion indicator.
'her majesty' becomes 'er' (Elizabeth Regina).
'che'+'leader'='cheleader'
'cheleader' going around 'er' is 'CHEERLEADER'.
'of' acts as a link.
(Other definitions for cheerleader that I've seen before include "figure offering vocal support?" , "Enthusiastic type" , "Dancing chanting supporter of US sports team" , "Organised team supporter" , "Head of an organised supporters' group" .)