I have worldwide travel insurance through Lloyds TSB bank account (premier) it costs of course, but for us the benefits far outweigh the cost. I had a look in the terms and conditions and it has a general section on exclusions which includes "the use of moped, motorcycle, car, van or similar unless a full UK licence is held permitting the use of such vehicles in the UK and in the case of a moped or motorcycle you and your passenger are wearing crash helmets". As I can see no other specific mention of motorcycles I take that to mean I am covered.
