Why wait till Christmas for school to do something? Your son needs significant support now. He can't afford to wait any longer for them to do what they should have been doing for the last 5 years.
From the sounds of it, your son has been failed big time. They didn't need to wait for a diagnosis - they should have been putting things in place long ago. They are a disgrace. 
How have they let him get to Y5 without asking the EP to come in before now or applying for an EHCNA themselves when he has all these difficulties? That poor child must hate going to school.
Apply for an EHCNA yourself with the IPSEA model letter.
www.ipsea.org.uk/making-a-request-for-an-ehc-needs-assessment
The legal test for an EHC Needs assessment is this:
If a local authority (“LA”) is requested to carry out an EHC needs assessment by a parent, young person, school or college, they must consider:
- whether the child or young person has or may have special educational needs (“SEN”); and
-whether they may need special educational provision to be made through an EHC plan.
Any other tests, like the school have to spend £6000 or they have to do two terms of this, that or the other intervention are LA policies and are unlawful. They are not allowed to set any other criteria. The only test set out in the law is the one above.
You've got enough evidence already to show your son has special educational needs, and clearly the school aren't meeting his needs, so he may need an EHCP -
He's 2-3 years behind, he struggles socially, has no idea how to make friends, has huge difficulty processing information and instructions, he has difficulties expressing himself, struggles with handwriting, has poor concentration and has significant difficulties with executive function.
It can take ages to get an EHCP as people on here will testify. (It's supposed to be 20 weeks
)
The sooner you start the process, the better. If the LA refuses, appeal. 90% of parents win refusal to assess appeals, and some LAs refuse as a matter of course and then back down when parents fight back.
Good luck 