The Hampstead Parish Lock-up
The plaque reads:
"About 1730, this lock-up was built into the garden wall of Cannon Hall, where local magistrates held court. Prisoners were kept in this dark single cell until more lasting arrangements could be made for them. Soon after the formation of the police force in 1829, business was transferred to the Watch House in Holly Walk.
This lock-up is one of the very few left in London and is a D.O.E. Listed building of historic interest."