Best advice I can give would be shop around I'm afraid!
Try confused.com, moneysupermarket, tesco etc - and also direct line as they don't use any of those - but also think about calling some other non-online companies too. When I was 18/19 my friends and I all had similar cars, same area etc - but a company that was cheap for one would be expensive for another - so just 'cos we got a good quote from one company they might be rubbish for you!
Oh yeah, but what ever company you go with expect to have your trousers pulled down with a Gti at 17!