-
That's technically a PA report the Grauniad carries. The application for a basement extension (among other things) is here:
Replacement of lower ground floor rear extension; lowering of floor slab at lower ground floor; excavation of basement storey under property and extension; replacement of two windows at ground floor with timber door set; replacement of window and door at front light well; and internal refurbishment
It was decided on the 30th April 2020. Maybe the researcher didn't know how to look for determined applications.
Digging out a basement I reckon, looking at the sign on the right