do haggle with them as hard as you can, pit them against each other e.g. can you beat this quote with this level of cover..... for that amount of money they'll be happy to have you on board, because at the end of the day, they are raking it in any which way, and one bloke popping up to try and negotiate a better deal fades into the general sea of those who blindly fill out the renewal form, enclose a cheque made out to the full amount, and curse as they put it in the letter box. better to keep customer relations up and fall short by a few pounds (on the chance you'll keep with them, paying a disproportionate amount of money at 24 compared to your much reduced risk) than stick solid and lose you.
and if they *do* want to inspect the car (never heard of it personally, not when it's not been pranged, but who's to say)...... de-mod it as much as you think they'll believe, and give it a wash a couple or three days before they come round (not just before! needs to have a *little* dirt..). try to look decidedly average, not someone who's going to "love" the car incessantly to the point of polishing it every day, whacking a big wing on it and going street racing, but neither one who'll never wash the car (even to the detriment of seeing out the windows) or maintain the engine at all, to the point where it seizes up on the motorway one day and causes a pile-up....... which they have to pay for a million or more out of your 3rd party cover.
just a thought
** edit -- another thought i had was, oops... p'raps he meant, because you were declaring mods
(that seizing thing? yeah... that was the girl that hit me... killed the escort's engine - on the m42 - by never putting oil in it, even though it was pretty obvious it had a busted gasket and was dropping large amounts all over the place. (un?)luckily, it was 3am and she made it to the hard shoulder)
PS Gti, what's an SP50??