Came accross these on Ebay earlier and they are a lot nicer than the usual lumpy number plate lights, only question is would they pass SVA. reading SVA manual only requirement is that the light is capable of illuminating the plate.

http://cgi.ebay.co.uk/Motrax-LED-Number-Plate-Light_W0QQitemZ8062087113QQcategoryZ25632QQrdZ1QQcmdZViewItem

According to the manual - as long as it's sufficient for the job.

I'm guessing radius comes into play as well.

but if it lights the number plate and conforms to radius - no reason why not

I'd be very careful as if you see the light source (ie Bulb or LED) you will fail SVA.