there is a lot of "it depends" on type answers there... you might start with a good travel agency like dreams unlimited, letting them know all your details and getting a base of reference... depending on how long you are going, an annual pass might save more than the cost in discounts. There are often specials and discounts for the UK. And UK has special ticket offers not available to the US.
I am from the UK too and I have always found out the best deals on this web site. Last year I got 40% off at Saratoga Springs which was fantastic. The year before I bought an Annual Pass which got me 30% off at Fort Wilderness. I would say in general you can get a much better deal booking directly with Disney in the US. I have never seen a deal on the UK website, other than free dining.