Muscle power, taking no prisoner, overwhelms East End bully (7)
I believe the answer is:
erector
'muscle' is the definition.
(I've seen this before)
'power taking no prisoner overwhelms east end bully' is the wordplay.
'taking no' suggests deleting specific letters.
'prisoner' becomes 'POW' (POW is an example).
'overwhelms' means one lot of letters goes inside another.
'east end bully' becomes 'recto' (I can't explain this - if you can you should give a lot more credence to this answer).
'power' with 'pow' taken away is 'er'.
'er' going around 'recto' is 'ERECTOR'.
Can you help me to learn more?
(Other definitions for erector that I've seen before include "Builder" , "puts things up" , "Muscle" , "The individual raising" , "One who puts (something) up" .)