A small minority of children who have needs defined as "severe and complex" may need to be supported via an Education, Health and Care Plan.
If the school and/or parents believe that the support being provided through School Support Arrangements is not meeting a child's needs, they may apply to the local authority for an EHCP. The application is reviewed by a panel and a decision is made. The local authority will then identify the child's needs specify the nature of the provision the child requires. Some additional funding may be provided by the Local Authority. In a small minority of cases, the local authority may decide that the child requires specialist provision (a place in a resource-centre within a mainstream school, or a place at a special school.)
There is a time-line in the 2014 Code of Practice which must be followed. You can find it on pages 151 to 154 of the Code of Practice document here.
You can see the EHCP request form https://www.surreylocaloffer.org.uk/parents-and-carers/ehcp