It would indeed by instructive to know that difference, not to mention highly enlightening. By the way, did you mean struck for the Festival of Britain, or were they actually struck at the Festival of Britain? If so, that's quite interesting.
What are your respective criterias, and may we see the coin in question to form separate independent judgements?
I don't know what to think, Pete. It's a very nice coin, but if I'm absolutely honest, not a proof. Specimen, yes - and described as such by Neil/Lee at the time:-