I am currently reading the Haynes Home Extension Manual which is
surprisingly readable and covers much of what I have been struggling to
research from various other books.

Howeve in the 'Planning & Building Regs' chapter it talks about 'right to
light' and the 45 degree rule - a line at 45 degrees to the corner of your
extension should not cover a neighbour's window.

Now we live in a semi, and all have a rear 'outcrop' which originally held
an outside toilet and coal shed. This complies with the 45 degree rule. In
many houses (ours included) this has been converted into a kitchen extension
by knocking out part of the back wall of the house.

Several of the semis on our side of the street (where we can see the back
gardens) have built all the way across the back of the house; extending this
'outcrop' sideways. This seems to conflict with the 45 degree rule as when
you build up to the boundary you must cast a shadow across the rear of your
neighbour's house.

So:

(1) Is this 45 degree rule recent? I can think of loads of extensions where
this has not been followed.
(2) Does it perhaps only apply to two storey extensions?
(3) Is there another rule which 'trumps' this such as one allowing full
width extension for a certain distance behind the house?

Oh, and is there another forum I should consult such as
'uk.rec.legal.moderated'?

TIA

Dave R