Thanks Nobby. Their policy certainly looks good - I especially like the bit that says they will cover you in countries that the FO says you shouldn't go to, so long as your claim isn't caused by the reason why the FO is giving the advice. I haven't come across this in any other policy and it sounds like just what I need - in my case it would cover me throughout Algeria, but claims resulting from terrorism would be excluded. This seems very reasonable and I wish other insurers would take the same attitude.
So I contacted Worldwide and after a week of deliberation they said they wouldn't cover me at all for solo motorcycle travel in the Sahara, even though I said I would stick to mapped pistes. They say it's just too great a risk. Maybe they are right! I suppose the chance of breaking a collarbone or a rib and then needing an evacuation are really quite high compared to the other risks they insure against.
So it looks like the best cover I can get is with Navigator, who are OK with the solo motorcycling in the desert, but won't allow any claims at all from countries that the FO advises against travelling to.
If a thing is worth doing, it\'s worth doing to extremes.