To comply with the current MOT inspection guidelines and BSAU 145d, although this is soon changing to BSAU 145e (which will not affect number plate dimensions), the smallest possible square registration plate sizes for imported vehicles consist of the following:-
226w x 156h (mm) – 7 digit reg
172w x 156h (mm) – 6 digit reg
172w x 156h (mm) – 5 digit reg
However, if any of your characters consist of an I or a 1, then the width of your number plate may be reduced by 34mm (for each 1 or I you have) as the character width can be 10mm as opposed to 44mm.
Note:- The reduction in size is subject to the formation of characters so this may not be available for some customers.