£200 cancelation fee? My premium for the whole year is less than that!
I think that definitely warrants a strongly worded complaint.
Insurance companies are just a law unto themselves when it comes to working out premiums. You'll go crazy tryng to figure out the logic behind them. It really does pay to call around. I can still remember quotes I was given on a particular vehicle about 17 years or so ago, simply because of the huge range from lowest to highest: A little under £110 at the low end and over £850 at the high end!
It certainly pays to go to the more specialist brokers if you have anything which could be considered even slightly "unusual" for the U.K., such as an imported car, non U.K. license, etc. Here's one you might like to try:
http://www.adrianflux.co.uk/(Can't guarantee what they'd be like in this particular situation, but they've generally been good on quotes for driving American cars here.)