I don't think it is wise to buy online as they will not be tailoring the insurance to your needs.
I use a broker and they review and shop around on my behalf every year.
(The first year I used them they saved me £150 on my previous year's premium)
All it takes is a phone call... a lot less time than shopping around on the net.
If you are interested, they are Newstead Insurance and their website is
http://www.newstead.co.uk/