Hihi, my views on personalised plates are on the same lines as G4GS's, but don't think I have to be rude, just because sombody has a different opinion.
In Germany they are very common, and not that expensive, but still I think it's waste of money.
A colleague of mine on has had a plate 'on hold for him' for several years.
He got a different (but similar) plate for a car that he thought would be temporary.
Now, years later, he is still driving this car, but has to check every three months, when his reservation runs out to make sure, that he renews it, before somebody else can get it.
Once, somebody else managed to reserve it after his reservation ran out, and for months, he was in a foul mood.
Then he managed to get it back...
This dedication is unbelievable to me!
But then, I always turn my car radio volume to an even number...
:o)
Sorry, to the original question: I am not sure, what the rules on English plates are...
I have seen H2O once, where the digit was a little smaller than the letters...
I'm sure that was illegal, but somehow cute!