In reply to gammarus:
I use a company called Voyager, through my broker. I currently have an annual world-wide policy to cover the family and I got a bolt-on extra bit to cover me for this year's Etape with increased cover just for the day of the event.
I've used them for years and they were great when I had to claim for a lost camera due to a ripped pocket on a ski trip a few years ago.
I should add they have different levels of policy, depending on what you're doing, and they cover off-piste skiing in the standard policy.
Post edited at 15:02