This delight is in Kingly Street, London, W1 at the back of the shops in iconic Regent Street. I have no clue if it is used or if so what for. Is it some night-dive? Or the goods entrance to one of the Regent Street Shops (unlikely; the road is pedestrianised)? Or a staff entrance? Why the padded doors, and fancy gates? Oh and note the tuft of grass on the top of the gatepost!
[Further research reveals that this is the Studio Valbonne nightclub. The state of the entrance is a fairly good guide to the reviews it gets.]