From Cheshire East Livewell website:
Education, Health and Care Needs Assessments and Plans
Education, health and care (EHC) needs assessments are for children and young people with the most severe and complex needs.
When to request an Education, Health and Care needs assessment
An EHC needs assessment is not the first step in the process of meeting the needs of a child or young person with SEN .
Most children and young people’s special educational needs will be met within mainstream educational settings at the SEN Support level. We recommended that you read information about Support  and consult the Cheshire East Toolkit for SEND  before considering an EHC needs assessment request.
EHC  needs assessment requests should be considered when the child or young person has not made expected progress despite a school or setting having taken relevant and purposeful action at the SEN Support level (as outlined in the Graduated Approach section of the Cheshire East Toolkit for SEND).
Who can request an EHC needs assessment

Your child’s educational setting (for example, a school, college or early years setting). This should be done with the knowledge and agreement of the parent/carer or young person where possible

A parent/carer. You will need to contact the SEND Team. You should first discuss your concerns with your child or young person’s educational setting prior to making a request.

Young people aged 16 or over with  SEN . You may wish to discuss your concerns with someone else before making a request for an assessment, such as your educational setting (school or college), parent or carer, or independent support services.

In addition, anyone else can bring a child or young person who has (or may have)  SEN to the attention of the local authority, particularly where they think an  EHC needs assessment may be necessary.
As a local authority, we will carry out an  EHC needs assessment for a child or young person if, after having considered any views expressed and evidence submitted, we are of the opinion that
(a) the child or young person has or may have special educational needs, and
(b) it may be necessary for special educational provision to be made for the child or young person in accordance with an  EHC plan.
To inform our decision about whether an  EHC needs assessment is required, we will need to take into account a wide range of evidence that describe the child or young person’s needs, rate of progress and the support that has been provided. Examples of evidence that we will consider are described in our checklists for EHCneeds assessment requests.