Poke to me is very different then :)
Legally I'm fairly sure as long as the tread of the tyre is inside the arch its fine, it might even be something like your allowed 15mm of tread outside the arch, its along time since I've done a MOT.
I really don't understand why everyone seems to think there is a problem with 25mm spacers.....
If there was "poke" then the tyre would contact the arch as the suspension compresses, which it doesn't...
Unless we have a very different opinion of what "poke" is.
Manders, I'm sure you might of already tried, but give Adrian Flux a call. Ive always insured my cars with them. I can never get insurance from other company's because of my modifications.
I have always declared everything to them and they have always been cheap!