One of our businesses is self drive hire.
Speak to Alan Boswell, they are a broker and have the SDH market sown up, they know all the underwriters for each specific application, they are good people to deal with.
Be warned, there has been massive hikes recently like all motor insurance, excesses have shot up, some people I know now have £1000 minimum excess, I have even heard that some underwriters are only taking on new clients with a minimum fleet of 5.
Expect to get shafted being new in a volatile insurance market.
This should have been the first thing you looked into because exactly how you operate an SDH business is dictated to you in your insurance agreement.