Avoid Adrian Flux at all costs, very rude, laughed when I tried to get insurance as a 21 year old on an Evo and said there was no chance in hell anyone would insure me until I was 25, point blank called me a liar when I said I already had a quote, and they even hung up on me.
They also refused to quote my mate (was 22 at the time) on an R32 GTS-t, saying "you won't be able to afford it", how the **** do they know that, he could be some little rich ****er for all they know, but they are so far up their own arses it's not even funny.
I wouldn't take insurance with them even if it was free, bunch of grade-A arrogant wankers.
I have been with Elephant for a few years now who have always beaten everyone else and are good for "young drivers" (under 25). Have heard really good things about Pace Ward & A-Plan, but they could not beat my quotes with Elephant so far, possibly because I am not 25 until next year.
Remember its not all about cost though, customer service is a must have too! Not only were Elephant the cheapest for me, but when I have needed them they have always been spot on.