Is there any legislation re the height of the plate?As long as there is 11mm at the top/bottom of the letters/numbers. Also at the sides of the plate.
And no minimum or maximum height from the road?
I don't think so. I think I read somewhere it had to be flat (or as vertical as possible)
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/359317/INF104_160914.pdf