OK @Spamfrit just a few thoughts.
If he is having intervention to get his maths up to a 7, an 8 on his very best day, I suspect A level maths is not a good idea. Maths teachers on these boards agree it should not be done with a lower grade than a 7, and if that 7 (while a fune grade) was hard-fought-for, it's probably not ideal.
Yes does he want to go to LSE? Or Oxford or Cambridge? Those are the main unis that specify in general specific subjects. While that's all good and those lists are useful, there’s no benefit to your DS taking physics (or whatever) when he hates it and won't get a good grade, just bc it's on the list.
It's important of course to take any subject that's needed for your uni plans – medecine? take chem and bio; engineering? take physics and maths; Eng lit? take errrm Eng lit.
A lot of degrees have no specific subject requirements.
What makes sense is to take subjects he likes that he is good at. I would say art may no0t be the best idea unless he plans to pursue it. Maths may be out of his reach tbh. English lit is great if he is good at that. How about another humanity – history, RS? A new subject like psychology, sociology, politics?
Despite some comments on here, there is nothing wrong with business A level (not Bus studies btw). Does he do it for GCSE? It can be done as a Btec - perfectly good – but the A level is also available and not a vocational subject to be looked down on. If he would do well and get an A, that's a lot better, and will open more doors, than a C or a D in maths tbh.