New MEES rules come into force for both EXISTING & NEW tenancies
Since April 2018, landlords have been unable to let their property to new tenants unless it has a minimum energy efficiency rating of an E (unless exempted) on its Energy Performance Certificate (EPC).
On 1st April 2020, this was extended to cover all existing tenancies as well as new tenancies, unless there is a registred exemption in place.
This means that anyone whose rental properties have EPC ratings of F or G are NOT legally allowed to let them out, unless an applicable exemption applies.
For more details https://www.gov.uk/guidance/domestic-private-rented-property-minimum-energy-efficiency-standard-landlord-guidance