Advise the insurance company that you will not be providing two estimates and that the vehicle will be repaired at your choice of repairer. The at fault insurer are obliged to provide and alternative vehicle or to cover the cost of hiring one. It is your vehicle, it is your lawful entitlement to choose how it is repaired and who repairs it. As long as the vehicle is repaired to the manufacturer's standards using the manufacturers methods, parts and paint and materials, under block exemption the manufacturer is not allowed to void the warranty. The best way of ascertaining whether the bodyshop is any good is by looking at their online reviews. I would also suggest if they hold the Kitemark for British Standards BS10125 they should be a very good repairer, though there are bodyshops without this that are as good or better. It may also assist you to contact the National Bodyshop Repair association who can recommend a manufacturer approved repairer in your area. You can contact them here: nbra.org.uk/