Pressed plates are legal, as long as they have the correct reflective material, correct spacing, font and character size.
A fully legal plate should have BS AU154 (or something similar) on it.
NEW plates (even if they are an "old" number) should have the maker's name and postcode on them too.
Without the BS number, they are technically illegal, but sometimes this is put in very small text, so not really visible from a moving car.
Sounds a bit harsh to me. Do you have any concerns about the legality of the plates?
I used to get pulled with my previous plate for being wrongly spaced (it was!) so I ended up spacing it legally. I was never fined or given a ticket for it. I used to keep a legal set in the boot, just in case. I never played dumb and said that I didn't know they were illegal. They were eventually sold with the car. I now have another private plate. And yes, it is illegally spaced, although not as radically as before. I never learn!!