Rest breaks

[Dana28]

Dd suffers from ibs which can cause a great deal of stress sitting in a large silent exam hall which caused her to develop an iety which makes the ibs worse which increases her anxiety. In the mocks and her a level exams so far she was allowed to stop the clock and take supervised toilet breaks. I have just had an email from school saying she must choose between small room and rest breaks OR access to a WC

That seems unaceptable to me, is it to do with the number of invigilators available to supervise the going to the toilet rather than actual JCQ regs I wonder?

That's just plain silly. Most of our small room cohort also have rest breaks (for various reasons). I would take it up with the exams officer and provide support from a doctor's evidence.

This will be the school trying to save money. Does access to a WC mean that the clock won’t be stopped when she goes to the toilet?

Rest breaks are clearly her usual way of working due to her medical condition - school can't remove them because of difficulties finding an invigilator.
Schools can make their own decision with regard to placing students in separate rooms as this is not covered by JCQ regs, but they must show consideration to the equality act in doing so. They have already put this adjustment in place so removing it at this stage could be considered to be a significant disadvantage your dd.

You could email back and say that any changes to her existing exam arrangements will significantly disadvantage her. Be clear that you expect her existing arrangements to be in place for her next exam.

Exam invigilator here. It is possible for a candidate to have rest breaks and have access to a toilet. The school where I work has cards for each and pupils can have either (or both) card(s).
The invigilators don't always know why candidates have these cards though and neither do the other pupils.
Possibly someone else (another parent or candidate) has complained that your dd has access to a toilet and theirs doesn't so it may not just be about saving money.