At the risk of peeing some of you off I thought I'd mention my recent experience of renewing the insurance on my Mk4 GTTDi 130PS - remap and modest lowering.
I am an old f*rt with a pretty good record and in a good area so the renewal quote with AXA thro Flux was £288, but I punted around and got down to 190 with Admiral. Went back to Flux and they managed 185 with Equity Redstar by reducing their commission (that showed up when I got the official documents thro and it said £20 odd more than I actually paid).
So I saved over £100 with an hour or so online and a few phone calls! If you don't ask you don't get....