Glad you asked mate Its now a private property and by chance as i was taking a photo the door opened and out came a chap suprised by me taking photos he asked what i was doing and i told him. He told me it is approx 180 feet long and 10 feet wide.he was in a rush so i didnt go down.
Intrigued by what it's being used for now... Steel door with a letterbox in it, couple of brown envelopes been posted through and lying on the top step. Ladder stored on the wall. Door at the bottom of the stairs seems to have a cutout 'Mighty Boosh' face stuck to it. Is that a cigarette bin down there? Hmm...
It is a very secure entrance/exit to a block of flats(once a very large house) and a fire exit. They seemed to use a lot of cellars for air raid shelters in WW2 ( and the rest of GB) I have take a number in London. The reality if the a parachute mine landed near im not sure the cellar shelters would have survived Air Raid Shelter Sign 15 Lord North Street, Westminster