Old British government in shock after revolution (3)
I believe the answer is:
raj
'old british government' is the definition.
(Indian term for rule or government)
'shock after revolution' is the wordplay.
'shock' becomes 'jar' (I've seen this in another clue).
'after revolution' says the letters should be written in reverse (letters revolve back).
'jar' written backwards gives 'RAJ'.
'in' acts as a link.
(Other definitions for raj that I've seen before include "Jar (anag.)" , "Sovereignty" , "British dominion over India" , "Indian government" , "Jar this rule in India" .)