Whilst this is not legally required, the HSE Management standards approach offers a clear and systematic framework to help employers identify, manage and mitigate stress at work. Other frameworks are available, e.g. ISO45003 (https://www.iso.org/obp/ui/#iso:std:iso:45003:ed-1:v1:en). Whatever you use, ensure it is a validated, evidence based framework.

Review these standards here; https://www.hse.gov.uk/stress/standards/