One of the last remaining Police Telephones still operational in a Police Post in Northwood.
Multiple signage indicates that this phone will connect with the Uxbridge Police Station.
I didn't get a chance to give it a try, but the location behind a Police Station might indicate its validity.
The same type of telephone a Ascom Bershire model, can be found in the Grosvenor Square Police Post. Although that phone has been disconnected since it was moved in 2008. Not sure if it was operational before that however.