School refusal

Our 10 year old son - diagnosed with 'mild but not typical' ASD in May - has refused to go to school since last November. The school is kind, nurturing and been amazingly patient and has tried everything - and currently has temporary funding for him to have 3 hours teaching at home with one of their teaching assistants each day. The plan is to transfer this to a library or cafe after a while, then into school, then gradually for him to rejoin the class. We have no idea whether this will work. A major issue is separation anxiety. It's very slow progress. Some days he works well with the teacher, on others it's very difficult to get him to comply. We've applied for an EHCP but no decision yet. We have to apply for secondary schools by the end of October - for a child who's not been to school for almost a year and who doesn't yet have an EHCP in place. Does anyone have similar experiences and what were your solutions to the school refusal? Or did anyone find alternatives to school? We live in London.