Thanks Dennis, it looks like I'll have to take a good look at the way we're set-up. In the UK I know that I can get a red/white striped triangle, but are you saying it needs to be a 50x50 square? Is the illumination white or red?

Cheshire, I don't know how they're classified, but I got pulled near home on my way back from Datchet last year and all was OK.