Just be careful here, Liv vic are the ONLY insurance company I know of who will pay out for your mods. Tesco, CIS etc all charge you more for having the mods on your car but WILL NOT (as of two months ago when I was ringing round) pay out for your mods.
i.e. if you have a 1.2 16v dynamique with 17" alloys, lowered 60mm, colour coded, induction kit, etc etc then tescos will charge you a whole heap load more for having it but if it gets nicked or written off whatever will only pay out the value of a standard car.
Liv vic will pay out the replacement value of all mods so long as you have photos as evidence.
Not sure about Adrian Flux on this one, I would assume they pay out for mods but dont take it for granted
and edde: So more than basically allow any styling mods but nothing performance related cos anything you do performance is gonna increase acceleration or top speed!! well unless youre me and fit a k and n and it makes it slightly slower!!!