On Fri, 4 Mar 2005 19:31:32 -0000, a particular chimpanzee named "Mike
Taylor" randomly hit
the keyboard and produced:

Your BCO was wrong
Your neighbour can only build on his side of the boundary and for technical
purposes the boundary goes vertically down and up form the ground. The
foundations have to be on his property so does any overhang, gutters, tiles,
window catches etc. You need to go backto your BCO and check the plans of
your neighbour's extension then talk to the BCO.

Two points:

1. The OP only talked about Planning, not Building Control.

2. There is no such prohibition in the Building Regulations about
building over boundaries. There are requirements relating to fire
spread and combustible materials on or near the boundaries, but it's
not for the BCO to determine where they are. IANAL, but AFAIK any
matters of trespass, etc., are civil matters.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"