That's good enough Stewie. It is the original entrance to the crypt which was bricked up as part of either the 1751 work or else the Cottingham work of 75 years later. The top of the stair is visible in the quire transept, quite handy for suggesting people look in there!
In the crypt the entrance was behind shelving in a store room. When they cleared the store room (as part of the investigation into the external Norman staircase under the Kent Stairs) they found a passageway and the steps leading up to a brick wall. Probably not been seen for the best part of a couple of centuries!
Anyhow, over to you Stewie.
