Thanks for all the advice.
We will check with the school.
Sounds like we will need to do some sort of upgrade. Checking online, the cheaper FX-991EX is said to be suitable for A level and the more expensive ones seem to be graphical whatever that means exactly (presumably draws graphs on the screen?).
Presumably the graphical ones offer more advantages, although I must say that I don't think its right that pupils from richer families studying maths A level would seem to have additional advantages over those from less well off families dependent on what sort of calculator they can afford!
I did maths A level myself a fair few years ago and we didn't require anything fancy other than the standard sine, cos functions etc that we already had on our GCSE calculators. In fact I seem to remember that certain fancy programmable calculators were distinctly NOT allowed in exams. Has the A level syllabus changed that much since then?