In some regions, the cost of renovating a property in line with net zero targets exceeded the annual rent for the average property.
In Wales, where the average monthly rent is just £804, making £10,000 worth of improvements would account for 104pc of a landlord’s typical rental income, leaving them “significantly out of pocket” after other costs and taxes, Hamptons said.
The company found that rents would need to rise by between £140 to £160 for landlords to recoup their investment, with sharper rises in the affordable areas.
Tenants in London face a more modest monthly increase of 6pc to £2,530, while those in the East Midlands could see rents jump by 17pc to £1,107.
EPC targets for landlords were previously floated by the Tories but ultimately dropped as part of a wider relaxing of green policies by Rishi Sunak.
Michael Gove, the then-housing secretary, said the Government was asking “too much, too quickly” by forcing landlords to achieve a C-grade EPC by 2028.
The targets are set to be reintroduced by the current Government, following Mr Miliband’s speech at the party’s conference, with grants only available to landlords who let to low-income tenants.
The energy secretary said it was a “Tory scandal” that Britain’s poorest households were living in “cold, draughty homes”, adding that “many rent from private landlords, below decent standards”.