The flag is usually not an issue. It's normally the raised text that features on German plates, or the idiots that put yellow plates on front and back. The cameras have issues reading them. Go for it if you want a £30 on the spot fine.
Some coppers will not know the law and let you get a way with it, an arsey copper may pull your pants down though. Some poeple put velcro on their jerry plates and attach the legal plates on to that, over the jerry ones. That way, if you get pulled, you say sorry Mr copper, my real plates are in the car, just been to a show..... Doesn't always work.
My gf has just put new plates on her car. UK spec with a black Seat
badge on the LHS. Goes well with the black car tbh.
Funny thing was, the website didn't ask for proof of addy, via v5, like they are supposed to. They need to put the post code on the plate or something.