I got a really good deal from here http://www.vaninsured...siness-van-insurance/ - if you call them direct you dont need to go down the comparison form filling route and they got a cheapest price guarantee.
As for the speeding convictions it'll add a bit (maybe £50) to the premium but dont worry too much, that many people have a few speeding tickets now that they dont increase the cost as much as they used to!