Hi Ian,
I too was a little apprehensive when it came to the maths involved with the ATPL examinations.
As I am only a third of the way through the first module I'm no expert but can honestly say that you shouldn't have any problems.
So far it is basic GCSE stuff such as Trig' (so far lots of it but very well explained in the notes) and forumlas. Knowing why and how to re-arrange formulas will help somewhat when it comes to subjects such as general nav, performance etc... but not at all difficult.
Go for it...
Best wishes,
Charlie Zulu.