Is there such a thing?

My insurance is up for renewal and at the mo i havent actually declared my car modified as it has only recently all been done.

Im with a crap company at the moment as th car was standard but now i want to move to a better one for modded cars.

Thing is, when i declare everything the insurance quote is gonna shoot up and then if it gets nicked then they're gonna give me about £200 book value for a Ford Fiesta.

So where do i stand - i dont want to do anything illegal but if im paying more - i wanna get a good payout.

Any help you can offer...?