The annual SEN statistics commissioned by the DfE have now been published and are available here:
https://www.gov.uk/government/statistics/special-educational-needs-in-england-january-2020
Headline facts and figures for 2019/20- 3.3% of learners have an EHCP and 12.1% at SEN Support
Overall SEN figure 15.4%
How does this compare to your data?