The Foundations workshops are mostly only given via our online platform (which means you can attend from the UK). Make sure to look through the description of what is covered on our web site - the Foundations workshops cover things like how to add, subtract, multiply, and divide fractions, or the basics of triangles and quadrilaterals - typically things we learned in school before the age of 12. They don't cover algebra or trig and only the basics of geometry. (The test itself doesn't test trig at all.)
We also offer our regular courses via our online platform. Our online courses and workshops are with live instructors and are exactly like the in-person courses, except that you are interacting via the computer. I've had people take my online classes from London, Sydney, Mumbai, South Africa... all over! You can sign up for a free session to see whether you like the platform and think it would be effective for you - check our web site ("Free Events") for details.
We offer a "boot camp" in New York City - you can do the entire course in 2 weeks. The next one will begin in early August. It's very intense, so make sure to read the description thoroughly to make sure that you think it would work for you. For many people, they wouldn't learn the material as well as they could if they spread the study out over a longer period of time. The other courses are spread over a 9-week timeframe; if you want to do the regular course, just pick a city and course (NY, Boston, Chicago, DC, Philadelphia, San Francisco, LA, and a dozen others - see our web site for the full list). You can also call the office at 212.721.7400 (or 800.576.GMAT from the US or Canada).
If you decide to do the Foundations workshops plus a full course, do the workshops first. The workshops are designed to get those students who need some extra help up to speed before the course starts.
Finally, you can learn more about signing up for the official test at
www.mba.com. You can sign up for the test on almost any day of the week; most people sign up 2-6 weeks in advance of their test date, depending upon how flexible their schedules are.