Forget about online 'Comparison' sites that spend a fortune advertising on television...if they have that much money to spare, think where it is coming from. They are paid on commission by the various insurers, and beleive me, they take a VERY healthy cut.
Grab your Yellow Pages and see if you have a branch of A-Plan or Swinton near you, and go in and have a chat.. When I insured my cars through A-plan I enquired about the best way to get insurance for EmmyLou in a year or two...they told me that if I were to insure her (at 17) fully comp in a Nissan Micra or similar it would cost...between £750 and £900 a YEAR! This would be her own policy in her name..not as a named driver on my policy...admittedly that would have been slightly cheaper at the start, but by the time she was 20-something then she would not have any NCB, so it was the best way to future cheap insurance for her.
(NOTE>>The guy DID say that girls got cheaper insurance than blokes because they are less likely to play Street Racers in clapped out bangers.....but then again, he doesn't know EmmyLou!!!!)