In reply to GrahamD:
My normal holiday insurance - Voyager - covers me for "normal" cycling, including road and off-road. That's what I used when I was cycling in France last year (following the last week of the Tour).
If you're racing or doing extreme downhilling, then worth getting specific cover. To be on the safe side, I did extend the cover specifically for a "race" to cover me for the Etape - it was twice the daily premium.