Brent borough council insist on battening and hence a generous air gap
over
brickwork with no waterproofing treatment applied directly to the wall :-

The Council are simply requiring you to follow current building control
standards. These change over time and what was considered appropriate ten
years ago is often different from that now required. These rules apply
across the country not just to Brent. Under certain circumstances they can
allow a particular job to be done in a different way if it is considered
appropriate.