It's an odd little nook. I imagine there's a quite expensive property back there. I've also never noticed the "OTF" carved into the near door pillar before.
Between the gate and the oriel, the keystone reads "The Mew House 1995".
The bricked-up door to the left seems to be an outbuilding in the incredibly grand-looking back garden of the Bishop's House. Speaking of which, here's a bonus pic of the Vicar of Clifton standing at the front door.
GPS Coordinates:
51.45400, -2.61375
Location: Cliftonwood