Just to be sure, did it look like this?
That's from the Truvelo UK website (Twister provided the links in
this thread which you might want to read as well).
The Truvelo site mentions that front facing cameras are fitted with a magenta filter, but doesn't say that rear facing cameras are. That suggests the filter is removable, and if some clown has taken it off that would explain why you got a visible flash. Still leaves the question of what speed it was set for though. If it was you that it got, you must have been unlucky and only just over the threshold.
You may still have a slim chance though. I found this picture on the Truvelo site as well:
Now that funny purply colour cast on the bumber, grill and door mirrors of the lorry, and on the borders of the speed limit sign and the Mini's number plate, make me suspect it is infra red film being used. I could be wrong about that, as I've never used colour IR film, and only just recently started playing with b&w IR.
Your slim chance, if it is IR film, is that the exposure might have been screwed up as a result of the wrong flash. The instructions on the IR film that I've been trying says that it can be quite hit and miss, and that you have to bracket a lot. If (and it's a big if) that applies to colour IR as well, and if (also big if) that's what your piccie is on, they may not be able to read your number. It all depends on the sensitivity of the film and whether they suss the missing flash filter and adjust for it in developing. It may be that they end up with a more or less normal photo without the funny colours. Or it may be that the colours are a result of playing with the image before putting it on the web. I don't know enough to say for sure so this is all ifs and maybes. I'll do some reading about IR film and maybe post a question on a photography forum about it to see if I can be more definite.
If you do get a NIP try and get hold of a copy of the photo and ask if you can see the neg/trannie. You may have something if the original is illegible but you've got a print out of a computer. I think enhancing images in developing or photographic printing is allowed, but in the computer it's a no-no. Someone will correct me if I'm wrong, or you could go over to the Pepipoo forums and ask there.
Edit: Oh yeah, and if they make waves about shwoing you the photo and orginal you might want to prod 'em by complaining about being flashed in the face at close range while you're driving. Defintely ask on the Pepipoo forums about it before doing that though. It's probably a good idea to aske 'em anyway if you do want to see the photo.
http://www.pepipoo.com