First the bad news
For most people (ie everyone except Cuba expats living in the US), the only flights that operate to Cuba from the most obvious jumping off point, the USA, are to Guantanamo Bay. This is due to a decades old American law that forbids any recognition or commercial interaction with Cuba. Anti-Cuban Government sentiment is so entrenched in U.S laws that if you have a flight to Havana booked on the same ticket as an American based airline such as Continental Airlines, US Airways or United Airlines etc., they will cancel all of your reservation, render your booking invalid, and refuse boarding on any of their flights. For example, if you fly with Iberia to Havana, take a separate flight on an entirely separate ticket to Montego Bay in Jamaica or to Grand Cayman, and then want to fly from there to Miami with American Airlines, you won't be allowed to! There is some hope that the more enlightened Obama Administration may change all this, though it is fair to assume that Barack has some other more pressing issues to deal with for now before this one rises to the top of his in tray.
Now the good news
By dealing with a round the world flight specialist such as Travel Nation, it is possible to include Cuba either at the beginning or the end of your round the world trip.
There are two key airlines in the round the world flights market that can be used to get between Cuba and the U.K. without going via the USA: Virgin fly from London to Havana on a directnon-stop flight twice weekly and Iberia have a daily connection via Madrid. The rest of this article will assume that you are flying round the world in a Westerly direction, though the same flights / conditions apply if you are flying in an Easterly direction.
If you fly out to Havana on Virgin, your next on that ticket will be out of L.A., San Francisco or Vancouver across the Pacific. To get there, 99% of people will need a separate bolt on ticket from Havana to Cancun (cheapest) or to Mexico City and make their way to the U.S. from there.
If you fly out to Havana on Iberia, you have the additional option of flying out on Iberia's fellow One World carrier, Lan, who operate a once weekly flight between Havana and Santiago in Chile. Otherwise, the next cheapest option will be to add a bolt on ticket to Cancun or Mexico and make your way from there (Lan Peru have an interesting flight from Mexico City to Lima in Peru for example). If you are heading to the USA having started your trip with a flight out to Havana on Iberia, the key thing to remember is that you won't be able use any American Airlines flights as part of your main round the world ticket.
As is often the case, the additional cost of including Cuba on a round the world ticket will usually work out at less than going there on a separate trip from the U.K., so if you have always wanted to go to Cuba, and are planning a round the world trip, check it out.
By Haydn Wrath of Travel Nation