Originally Posted by Elliott

The size of the plate is determined by law in a sneaky way.

Each character has to be a certain size and have a certain size gap in between.

Hence the 9x8 plate. However 99% of police are ok with a 8x7

Edit : just realised I didn't answer your question. I buy them from a MOT garage near me but you get the delivered for around £6 on eBay.