What a distressing time for your family. It's also a sad reflection on the difference between 'having policies in place' in a school, and actually doing something about an issue.
Depression at any age is a disability, and it might be helpful to your case if the disabling aspects of your son's mental distress become recognised.
Here's a few things you could try.
Get an appointment with GP and ask for a referral to another child psychologist. Explain that CAMS input has been ineffective. You've not been given any strategies for addressing son's needs. You must state your son's suicidal outlook in this session.
Might from the sound of it be good to take a break from school and schooling, which again should be discussed with the GP so it can be covered as illness, not unexplained non-attendance. I'm not saying home school him at this point - I'm just suggesting that not having to face what he finds an ordeal might help him heal a little.
A meeting with the headteacher would be in order, to ask if you could go through the notes and other information pertaining to your son. Make this a long meeting - emphasise to the head it may take some time but it ground you need to cover. take copies of everything you can at this meeting.
If it is a school run by the local authority, contact its lead adviser and ask for advice directly, mentioning that so far school and CAMS have not helped son's frame of mind, that he is suicidal, and that any support with alternatives to mainstream schooling and psychological counselling would be helpful. The notes you get from school would be helpful in dealing with the local authority.
During the down-time away from school, see if there are any activities son can become enrolled in that are both absorbing, and take him out of himself in a non-competitive environment.
You definitely need expert advice about when and whether he should phase back into school. It might be helpful to your son for you not to focus on entering mainstream secondary school as an immediate need. The transition from Y6 to Y7 can be stressful for kids at the best of times - but this is not the best of times for your son.
If he can use the internet, he can keep up with the knowledge base expected of an 11-year-old, so don't get anxious about 'missing schooling'.
You may be personally anxious about having to go to work, say, and leaving him unattended. If this is a source of anxiety again raise it with the GP, as it may be possible through a variety of young peoples' services to get help from a carer.
Best of luck with this. It will not be easy, but it isn't easy now, so brave heart, and love that lad.