sorry for the size of the pic and the quality, but Ive got this plate (well, its actually on the missus's fiesta now - Ive got my own plate back on mine).
Ive been pulled for this in Chesterfield, but Ive been followed by coppers in Sheffield several times and they didnt seem that bothered. I think it all depends on the copper, and the regional forces priorities. In Sheffield (South Yorkshire) they dont seem too bothered about minor things like this, but in Chesterfield (Derbyshire) they seem to be really picky about any motoring offence.
To be honest unles you change something else in that plate I wouldnt expect you would have too much bother.
The only real reason the feds are bothered about thses plates is that the specs cameras sometimes cant read them. But try getting a copper to admit that.