I think the plate looks ok. I got given the DVLA rules on plates from the coppers when I got pulled for VERY small front plate.
As long as the letter style, size, spacing and border are legal then that's fine as far as I read.
I'd look into it if I were you.
In fact - here you go buddie. http://www.dvla.gov.uk/media/pdf/leaflets/v796.pdf