If not, might be best to wait until you get there, and rent from a local office. I've done this a couple of times, and found it cheaper then pre-booking from one of the majors.
Unfortunately, I can't recall the name of the companies I've used.
www.holidayautos.co.uk are unique in that they cover the full CDW with no excess. The difference may be payable locally but they guarantee to refund it to your credit card @ end of the rental period, regardless of whether you have a claim or not.