I've just had a letter to that effect from TC this morning Mark for our booking.
Basically the letter says that cuba have introduced strict requirements to ensure holidaymakers have an insurance policy with appropriate medical cover and that Random checks will be made on arrival in Cuba so it is essential that you carry your documents in your hand luggage. If you do not have sufficient medical cover then you will be required to purchase a cuban policy on arrival which doesnt cover high risk sports or pre existing medical conditions.
It also reminds me that any policy underwritten by insurance companies of the united states will not be valid in cuba and that if you have purchased TC insurance underwritten by either White Horse or AXA then this is acceptable.
I will be double double checking with insureandgo .