Hundreds of thousands of buy-to-let homeowners will have to pay a “green tax” of up to £5,000 to make their properties more energy efficient, the Telegraph has learnt.

Landlords will have to pay upfront for measures such as insulation, cavity wall filling and new boilers from 2018. Until recently they could apply for loans from the Green Deal scheme for improvements, which are then repaid by tenants who benefit from lower bills. But the new Department for Business, Energy and Industrial Strategy is proposing owners provide the money.

The move will affect 330,000 buy-to-let landlords who own homes that are less energy efficient, often from the Victorian and Edwardian eras.