I am not sure of the exact position regards private schools but in the state sector your only responsibility is to inform the school, it is their responsibility to inform the LEA.
You are legally required to provide an education suitable to age and ability. Education is a very, very different thing to formal schooling.
We are relatively structured by most home educators standards and we spend approx 1 1/4 hours a day, 4 days a week, 32 weeks a year on maths, English, Latin and Spanish. Everything else we cover through hands on projects, reading, documentaries, museums etc. We spend a lot of time with friends and family. I allow a lot of time for hobbies and following his own interests. Lots of coding at the moment.
I find that this is more than sufficient to provide a deeper, richer education than school. We do not use the National Curriculum at all (primary motivation for home educating).
I do not know the background to your decision but sounds like your son has had a traumatic time of it. The most essential aspect of education is emotional well being. Read about deschooling, pretty much everyone (Inc LEAs now) recognise the value. It doesn't mean that nothing educational happens but that you let your child lead the way.
You have about 5 months. 2 months of which would be school holiday and a lot of the remaining time given over to tests, revision, end of year, shows, sports events etc.
In your shoes I would be making a list of places to visit while places are quiet, looking at local events, perhaps booking a holiday or short break. Work on providing the sort of enrichment activities that classrooms can't provide.
Find a project that appeals to him and will excite him. In this house I'd go for Raspberry Pi but something like a woodwork kit or camera or animation software or an online course in something that really interests him are all good. Something he can get in to and self teach and throw time and energy into.
I wouldn't worry about traditional school subjects for this length of time and at this point in his schooling. I certainly wouldn't spend money on workbooks or curricula. If you feel that gaps need to be plugged or he needs confidence building before secondary then look at something time Khan Academy.