The department collects information in the school census on pupils identified by their school as having special educational needs (SEN). Pupils with SEN either have an Education, Health and Care plan or receive SEN support as identified by their school. This is not dependent on a clinical diagnosis.
The latest data are published here: https://explore-education-statistics.service.gov.uk/find-statistics/special-educational-needs-in-england. In the latest data, schools in Romford constituency recorded 1,637 pupils with SEN.