Assuming he's in year 11, there's one month until the last exams (and a week of that is half term). Arrange with the school an early exam leave and just concentrate on getting there for the exams.
If he's refusing the exams themselves, he needs to understand that whatever else he wants to do, he'll almost certainly be studying English and maths on top of anything else, for the next two years (until he gets a C in both). He will be obliged by law to be in some form of full time education or training/apprenticeship/employment. And if it's anything at college or an apprenticeship, he will be forced to do the English and maths. far better to get them out of the way now.
The rest of his subjects are less high-stakes, but he's spent two years on them, so it seems a shame to throw that away.
College courses and apprenticeships will only be open to him at level 2 (like the btec first mentioned above), but that's the same standard as GCSEs. If he wants to do a level 3 course (like A level standard), he'll need to sit his exams this year.
I'd come at this from a career planning perspective, or if not career, then "soft ambitions" - in ten years does he want to have his own place? Work in a office or outdoors? Live in London or travel?
Might be worth asking if his school can make him an emergency careers appointment.