Also is it still legal (or was it ever) to mount the front plate on the front of the roof rack, on the bulkhead under or over the screen, a stick on type on the front of the bonnet or hung under the front bumber (so it whent flat at speed and avoided speed cameras)
So many questions, so few answers
Interestingly the UK Govt published a lot of stuff about the size, shape, font, letter spacing of the actual plates but not a lot on where you can put them. Going back to the original legislation you find that the requirement is that the plates, front or rear be as vertical as possible and visible from set distances. Nothing about the physical location.
Extract from: The Road Vehicles (Display of Registration Marks) Regulations 2001
Fixing of front registration plates: vehicles registered on or after the relevant date
6.—(1) This regulation applies to vehicles, other than works trucks, road rollers and agricultural machines, first registered on or after the relevant date.
(2) Except as provided in paragraph (5), a registration plate must be fixed on the front of the vehicle in the manner required by paragraph (3).
(3) This paragraph requires the plate to be fixed—
(a)vertically or, where that is not reasonably practicable, in a position as close to the vertical as is reasonably practicable,
(b)in such a position that in normal daylight the characters of the registration mark are easily distinguishable from every part of a relevant area having the diagonal length specified in paragraph (4).
(4) The diagonal length of the relevant area is—
(a)in the case of a mark having characters the width of which is at least 57 millimetres, 22 metres,
(b)in the case of a mark having characters the width of which is 50 millimetres, 21.5 metres,
(c)in the case of a mark having characters the width of which is 44 millimetres, 18 metres.
....and the same distances and "near vertical" for rear plates too.