Risk registers are documents that allow a school's or trust's leadership – which includes the governing board – to plan for, track, and monitor key risks and risk controls for the whole school or trust.
Risk registers are mandatory for academy trusts
This is set out in paragraph 2.35 of the Academy Trust Handbook
If you're in a multi-academy trust (MAT), there's no rule on whether you need school-level registers as well. It's about what works for you as a trust.
Keeping 1 trust-wide register means fewer documents. It also reinforces the fact that your trust is 1 organisation, not lots of separate entities.