As you may know you have to supply photos of classic bikes entered. One year they wrote back to me saying my exhaust didn't meet regs and suggesting I should fix it before arriving. I put a protractor on the photo and measured it, and as far as I could see I was spot on the limit. But knowing the wisdom of not arguing with scrutes I had the tailpiece modified. Sure enough there was a note on my scrutineering card to check the exhaust.

I've seen a few bikes with silencers pointing "illegally" upwards (modern ones, as it happens) and they have been commented on, but I've not seen one fail scrutineering yet.

Strikes me as a farly trivial rule TBH, I don't know why they are so bothered about it.