Hi Fraggle,
Your poor son! As the school hasn't been effective at putting a stop to this, maybe it is time to give up on this school and move on. Does he want to leave school?
Is he Year 11? Academically, it's an awkward time to start home ed, as he'd have to shift over from GCSEs to IGCSEs and if he wants to do those this year then you'd have to scramble to get it all arranged. However, there's no requirement to do exams at all, and if he does do them he can do any number - kids who aren't aiming for uni will probably find 5-6 are enough - and it doesn't have to be this year.
Another alternative is college, either right away or next year after a year of home educating. Some colleges have dedicated full-time or part-time (vocational day release from school) 14-16 provision. Others will accept a home educated child to study part-time alongside older learners if they seem ready. There will be some courses he can begin at college next year without having done GCSEs, while working concurrently towards a few GCSEs at the college. He may not get bullied in the different environment of college, or the college may be more effective at dealing with it than his school was.
Despite you working full-time, you'll manage the academics he needs. It's a matter of helping him find the right resources for what he wants to do, helping him with his studies if he gets stuck, and providing reassurance and encouragement.
If I were in your shoes I would be a little concerned that your son might feel somewhat lonely and isolated if he can't get out of the house enough. He won't have you there to keep him company during the day. Many people spend all day alone, but if it isn't by choice then it feels different. Think what you can do to tackle this. Can he get out by himself; does he use buses? If so, you and he can think of some things to get him out of the house regularly - swimming, library trips, shopping, paid or voluntary work. Even if that isn't possible, he still might prefer the less-than-ideal situation to his current school life, especially since he has no friends at school. The fact that he has already established out-of-school clubs he can continue is a big bonus and that should keep him ticking over adequately. Maybe he'll want to start some extra hobbies in the evenings or weekends when you can take him.