Well, from 1st November 2008 that is changing and it will be an offence to supply these non-standard plates.
http://ezinearticles.com/?DVLA-Number-P ... id=1390143From 1st November 2008 it will become an offence to supply number plates that do not comply with the road vehicles act (Display of Registration Marks) Regulations 2001. There is a maximum penalty of £2,500 and/or suspension from the register for up to 5 years. This offence will apply throughout the United Kingdom.
If you prefer to run your own personal risks of displaying a non-compliant plate, then that option will quickly disappear - at least when you buy a new vehicle (or some vigilante git breaks your "show plate" out of spite and you need to replace it)
I guess the only real way round this is to sign up NOW for a personal registration that you transfer to every new vehicle you buy (in turn - not all at once) - having first made up a lifetime's supply of "show plates" before the 1st November deadline.
BTW I carry a fully compliant plate and always have done .... however, such stupidly over-officious petty regulations make me want to consider ways to get round them (as per the above).
..... and also I'm not suggesting anyone should go ahead and display a non-conforming plate - of course!