The message
from "Brian Sharrock" contains these words:

With agreement; it's OK for the footings to extend into your property
- with
your permission - but the wall should not go beyond your property line. If
nothing occurs then after twelve? years the neighbours (may not be the same
people) will have gained your property by 'adverse possession.

The law on adverse possession differs these days depending on whether or
not the title is registered.

AIUI (IANAL) the time limit is down to ten years for property with
registered title but any claim will result in the Land registry
informing the registered owner who then has 2 years to evict the
squatter. If the registered owner chooses to do nothing then the
squatter can make another application after the 2 years have elapsed.

Traditionally squatters have had to wait 12 years (or 30 in respect of
Crown land) to claim title by which time the real owner has lost the
chance to evict, assuming the squatter can prove possession for the
required period.

--
Roger Chapman