As stated by Colin, I think it is very important to use a reputable specialist motor trade insurance broker, who can if he is truly impartial, place you with a proper company and give you the benefit of their buying power, and their expertise if it all goes wrong.

We have just renewed ours, and looked at many options, but if you are not carefull you could find you are under insured, because someone is trying to get the business, and not really worry about your best interests.

We have luckily never had to make a major claim, so perhaps these words of wisdom mean nothing, but hopefully if it does all go wrong, I have done the best I can to cover my a**e.
Andy