MEES
The rule making it unlawful to continue letting a domestic property in England and Wales rated F or G.
Since 1 April 2023 the Minimum Energy Efficiency Standard applies to continuing tenancies, not just new ones. A landlord holding an F or G must improve the property or register a valid exemption.
It does not extend to Scotland or Northern Ireland. Assuming it does would treat compliant landlords there as though they faced a deadline they do not have.