Flat to the wall is covered by permitted development, though still within the 200mm plane, so anything other than vertical would require planning permission.
What is says is :
"Permitted development
A. The installation, alteration or replacement of solar PV or solar thermal equipment
on—
(a) a dwellinghouse or a block of flats; or
(b) a building situated within the curtilage of a dwellinghouse or a block of flats.
Development not permitted
A.1. Development is not permitted by Class A if—
(a) the solar PV or solar thermal equipment would protrude more than 200 millimetres beyond the plane of the wall or the roof slope when measured from the perpendicular with the external surface of the wall or roof slope;
(b) it would result in the highest part of the solar PV or solar thermal equipment being higher than the highest part of the roof (excluding any chimney);
(c) in the case of land within a conservation area or which is a World Heritage Site, the solar PV or solar thermal equipment would be installed on a wall which fronts a highway;
(d) the solar PV or solar thermal equipment would be installed on a site designated as a scheduled monument; or
(e) the solar PV or solar thermal equipment would be installed on a building within the curtilage of the dwellinghouse or block of flats if the dwellinghouse or block of flats is a listed building."
and here's the rub:
"A.2. Development is permitted by Class A subject to the following conditions—
(a) solar PV or solar thermal equipment shall, so far as practicable, be sited so as to minimise its effect on the external appearance of the building;
(b) solar PV or solar thermal equipment shall, so far as practicable, be sited so as to minimise its effect on the amenity of the area; and
(c) solar PV or solar thermal equipment no longer needed for microgeneration shall be removed as soon as reasonably practicable."
Someone may justifiably have a complaint based on (a) or (b)