1 April 2018 saw the introduction of the Minimum Energy Efficiency Standards (MEES) for domestic and commercial rental properties.

Any new tenancies must have an EPC grade of E or better.  From April 2020 all domestic existing lets must achieve at least an E.  Non-domestic date is April 2023.

There are penalties for non-compliance but, also grants for insulation, heating and lighting.

There are exceptions and more detail to MEES; which is linked here and can be explained if you call Mark at Assess Energy Solutions UK

Elmhurst Energy factsheet MEES - Private Rental Sector - Landlords

Elmhurst Energy factsheet MEES - Tenants