SMI for council tax and mental health

For issues specific to caring for someone with mental ill health.
I have been told I am entitled to the SMI due to mh,my dr refused to sign the form so gave up I did reply and he never received his form he filled in so I gave up,I have spoke to him today and told him I fit criteria he said the form had changed and I said no it's still same form, he said bring it in a with the form he signs so it does not get lost ,I rang council and they said they will send his part to myself and form is still the same,what I want to ask is can someone explain the social functioning and the impairment of intelligence as I can't find no information on it only information is benefit and diagnosed by a dr.
SMI is usually taken to mean someone who does not have mental capacity under the Mental Health Act and covers conditions like dementia, Downs Syndrome or another severe learning disability.

you can download the full Mental Health Act here (beware it's very long !).
It's not just people with dementia or Down's syndrome,it includes depression ptsd bi polar and other things,I shall look at that to see if it answers my question
Hi Tracie
from my understanding Severe Mental Impairment does not sadly include depression , Bi polar , anxiety et . It is intended fo rpeople who lack mental capacity. It is extremely hard to get a Dr to even agree that a patient with early signs of dementia is SMI even though it is progressive. They will not usualy sign the form until a formal diagnosis has been made by the memory clinic of Dementia . If anyone is able to get a Dr to sign for anything else I think they are very lucky but I certainly wouldn't count on it.
If you handle all your own financial affairs, write intelligently on this forum and run your own day to day life you are certainly not SMI.
Hi henrietta thanks for the reply,it was seen on here that some councils use the term to define depression dementia and bi polar and are entitled to SMI,I am not saying I am or am not I wanted my question answering about intelligence what that would cover and social,and no I don't deal with day to day things without support and if it was not for the support I would not pay my bills or eat.
I am not aware these terms "intelligence" and "social functioning" have been legally defined in CTAX legislation so I think it is a matter of interpretation by the GP.
What is a severe mental impairment? Someone who is considered to be severely mentally impaired has a severe impairment to intelligence and social functioning (however caused). It must be a permanent impairment.
I think it's that word "permanent" that generally excludes conditions like depression which in many cases come and go according to the efficiency and response to treatment options.
They now include depression bi polar and other issues such as ptsd,I know of two people that claim it for mh issues.