Hi James,
Well, aren't you lucky? Three visits to Walt DIsney World this year sounds absolutely wonderful! If I were you, I would consider purchasing an
annual pass to Walt Disney World. Typically, an annual pass will save a guest money if they plan to visit the parks more than ten days in any calendar year. If you think you might visit the parks more than ten days over the course of your three visits this year, consider purchasing an annual pass. Annual pass holders have the added bonus of enjoying a nice variety of discounts (on dining, merchandise, tours, etc.) throughout Walt Disney World. Premium annual passes are also available if you wish to have unlimited access to Disney's water parks and DisneyQuest too.
If, however, you know you will only need seven days of admission to the Disney theme parks spread out over the next twelve months, the no expiration option may be the way to go. There is a great page as part of the Disney website that helps you calculate the difference between tickets with and without various options. (Select "buy park tickets" under the "tickets & packages" tab at www.disneyworld.com). When I used it to calculate the difference between a 7 day pass (with the park hopper option and access to the Disney water parks) with and without the no expiration option, the tickets with the no expiration option cost $160 more per ticket. If necessary, you can add days to these tickets while on vacation, but remember that you'd be better to purchase an annual pass if you plan to add more than three days.
Also, I recommend that you check with a travel agent in the UK to see if there are any discounted tickets available to overseas guests. It's always good to check all of your options.
Wishing you safe travels in 2012. Have a magical time at Walt Disney World!
Jill