I make aluminium pressed plates, with the legal british (charles wright) font. I provide small clear stickers with black text on the bottom with my manufacturers details and BS standard, so technically they are legal
The black/silver metal were upto 1973 and then white/yellow thereafter with the old charles wright font which was in use until 2001 when the GB Euro badge was brought out 
Hi Eliz. Thanks for the info. So are the yellow and white aluminium pressed plates legal on post 2001 cars? Also is there any chance of making the front plate the minimum legal size(aluminium style plate)? i.e. only 11mm from the edge of the plate to the edge of the lettering? I don't want loads of space either side of my number plate if possible.
metal plates have a black embossed edge all the way around so I could not alter them sorry. You could possibly try a DIY but they could end up looking quite a bit of a mess
I think the main concern on the legality of plates is legal size, font, reflectivity, spacing and manufacturers details being on.