Peter Taylor wrote:

Exemptions from Planning Permission are listed in the Town & Country
Planning (General Permitted Development) Order 1995. Porches are
permitted unless:

(a) the ground area (measured externally) of the structure would exceed
3 square metres;

Anyone know if the profile of the existing doorway is

+---=========---+
| |
| |
---------------+ +--------------

and a porch was build like this

E F
+---=========---+
| |
A | | B
---------+-----+ +-----+--------
| G H |
| |
| |
+---------=========---------+
C D

Would the 3m^2 area refer to the rectangle ABCD, or the sum of the
rectangles ABCD and EFGH? I would assume the former, on the grounds that
you could initially brick up G-H and move the door forwards, then build
the porch, but ....