Old Nick, in London (7)

I believe the answer is:

newgate

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'old nick' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for newgate that I've seen before include "Stir in capital" , "London street" , "Former London prison" , "Notorious 18th-century London prison" , "Old Nick" .)

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