VW Insurance were actually fairly competitive last year when I first got my GTI. Most insurance companies were coming out at about £1,200 and VW quoted me £979 (after a bit of haggling). In the end I went with Sky Insurance (one of the forum sponsors) for £850.
This year I've switched to Endsleigh for £630.
It definitely pays to spend as much time as you can using all the comparison sites, going direct to those not on there and considering specialists like Sky Insurance.
(I'm 26, the insurance covers me and my wife, we live in North London, 4 years NCD, 12,000 miles per year including business use.)