Phil L wrote:

The brushes are put down from top to bottom to stop the insulation spilling
into next doors cavity, which by law is classed as trespass, and this is
what causes damp, because 'their' insulation will not go from DPC to
roofline as yours will - it's only when insulation is stopped halfway up a
wall that water can track across from outside brick to inside block.

How do these brushes get fitted, out of interest - through holes? How
do they get into position?

David