I use NFU and they are really good. Admittedly i am abit older than 17 at 21 so your daughters will be more. Also i found this website that gives you 17 tips to lower your insurance quote, 17 wierd i know, but it was very helpful i wouldn't recommend using all the tips but if you just use a few it should really help to cut the cost. One of the tips is to buy your quote over the internet apperantly it is cheaper because it saves them time from phone calls.

The website is http://www.ascon.demon.co.uk/insurance.htm

It has quite alot of helpful advice and is very informative. I hoped this helped