From Pistonheads:
There is no regulation governing the size of the plate, only the size of the characters, spacing, and borders.
There is a specific exemption allowing the smaller characters on grey imports from Japan, etc:
http://www.legislati...gulation/5/made
Import Cars - Know the score with the plates!
https://www.craigspl...t-number-plates
Size and spacing of characters: special cases
14A.—(1) This regulation applies in relation to any vehicle imported into the United Kingdom which—
(a)does not have European Community Whole Vehicle Type Approval; and
(b)is so constructed that the area available for the fixing of the registration plate precludes the display on the plate of a registration mark in conformity with the requirements of regulation 14.
Note the 'and' in (a) above. It means that (b) must also be satisfied to qualify. Failing that the normal regs as to character size, spacing, and borders apply
The only way to be sure how small your plate can be is to take the number of characters in your VRM and do the maths. This will determine the minimum size of backing plate you can have.
Edited by mab01uk, 25 December 2013 - 11:37 PM.