Ask a Doctor and Get an Answer to Your Medical Question ASAP
Most likely your son has schizophrenia, which often manifests during the teen years.
Since you live in the UK, your son should be evaluated and treated by a community mental health team (CMHT) or an early intervention team. I believe your GP is the person to refer him there.
You can read more about schizophrenia and care here http://www.nhs.uk/Conditions/Schizophrenia/Pages/Treatment.aspx
I would call your GP and urge that he/she refer your son. There is good treatment for schizophrenia today, but it's not easy and requires help from a number of resources, as outlined on the website I listed. Best wishes to you and your son.