The significant majority of mortgaged residential properties currently below Energy Performance Certificate band C could achieve band C or above by investing less than 5% of the asset value.

That’s the verdict of environmental consultancy Kamma, and it becomes particularly relevant to the buy to let sector as Labour looks set to make band C the minimum grade for private rental properties should it form the next government.

Kamma analysed 200,000 mortgaged homes below an EPC C standard, and found that only 16.5% had a less affordable route to Band C.

More than half of the 83.5% could achieve Band C at a retrofit cost of less than £5,000, and 18% of properties would require under £750 in energy efficiency improvements.

Kamma chief executive Orla Shields says: “Out-of-date retrofit cost estimates are holding back progress across the whole property industry. Most lenders and homeowners rely on retrofit recommendations, installation cost estimates, and energy bill saving estimates from the property’s EPC certificate, but EPCs use cost baselines that are over a decade out of date.

“Better data on property carbon emissions overcomes the perceived cost barrier, increases action and unlocks the benefits of retrofit for homeowners and lenders alike. It’s not just homeowners that stand to benefit from retrofitting.

“Insulating homes reduces bills and insulates lenders from the increased risks associated with lending on under-performing homes. Changing regulations and changing buyer preferences both provide good reasons to act. With better data better choices can be made.”

Last week Labour deputy leader and shadow housing secretary Angela Rayner said if her party won next week’s election, it would require all landlords to make their properties EPC rating C or above by 2030.

Last autumn Prime Minister Rishi Sunak ditched EPC targets for the private rental sector, citing unreasonable costs for landlords.

Building on broad pledges contained in the Labour manifesto, the party now says private renters will be £250 a year better off under a Labour government after it forces landlords to improve the energy efficiency of rental homes.