[http://www.lgo.org.uk/news/2011/sep/councils-not-let-down-children-school-special-reasons/ here]] is link. Then download the focus report at the side.
You should also ring IPSEA on NAS education line.
You also need to apply for the statement yourself now. IPSEA / NAS will help you step by step.
You could ask the SEN officer to arrange PT or FT home tuition now to ensure he continues to have a FT education until he is back in school fully. You have more come back against the LA if they do not do anything than the school. Governors have no legal duty to meet your child's needs they only have to use their best endeavours. the LA has a legal duty to ensure a child's SEN are met. So you do need to make sure the SEN officer knows what is going on eg by requesting a statutory assessment (draft letter on IPSEA website) and set out that out of school due mental health / refusal.
You don't need your school's support to apply for a statement. The very fact he is only managing a few hours here and there is good evidence he needs a statement.
I understand you may worry about education social worker saying it is your fault you are not sending to school. You are right they may threaten you and say you should send him to school. But thats going to come out anyway when you try and get a statement / get him back to school. Try and CAMHS on your side and make sure something is in writing / in his CAMHS notes or even that you just sit down and write to CAMHS and 'confirm' the advice they gave you and see if they will agree he is out of school for mental health reasons / anxiety.
What does he do when you try and get him to school and he doesn't want to go? Is it something which you could video to show his reaction?
You need to start compiling evidence in writing etc If the school ever ask you to come and get him early that is an unlawful exclusion and you should ask for reasons in writing to prove he is being excluded.
Used to be guidance on Dept of Education website on home ed, looks like it has vanished it says the LA has discretion whether to help you financially if you home educate (ie you choose to home ed rather than ask for home tuition).
Are you likely to be eligible for legal aid? If so you could get an education lawyer to help you especially if you apply for a statement and it is refused - then you can appeal and use legal aid to fund private reports. I don't think you can get reports unless you have to appeal. Most legal aid lawyers will give free initial advice as to whether you might be eligible.