In reply to deanr:
If you want to do a formal course my first port of call would be your local college. They may offer adult education but if they don't they will know who does.
Another good one would be your local councils website and look at adult learning.
Personally I'd go for a teach it yourself approach. There are lots of good revision books for maths at A-level. Get one or two of those and work though them. You will probably find it not too tricky, and if you want the formal qualification I would imagine it not too difficult just to sit the exam.
Also worth considering are the free online courses offered by some american universities. A calculus 101 or similar might provide the correct level of difficulty.