The government has set a goal for as many homes as possible to reach a C rating by 2035, with an earlier target for private rented homes to reach the standard by 2030.
The study by Rightmove analysed the energy efficiency ratings of more than 15 million homes. It looked at the proportion of homes rated D to G, and showed what percentage had to potential to improve to C or above.
It found that across England and Wales, 41 per cent of homes have a rating of C or higher and there is potential for this to rise to 89 per cent if improvements are made.
The study further discovered that 11 million homes have no EPC rating, as they have not been sold or let since the certificates were introduced.
The areas currently having the highest proportion of homes rated C or above were Tower Hamlets at 73 per cent, Hackney at 39 per cent and Southwark at 58 per cent.
Those with the lowest proportion of C or higher rated properties were Gwynedd in Wales, Castle Point in Essex, and Pendle, Lancashire – all at 23 per cent.
In terms of the capacity to reach a C rating, Crawley was top, with 95 per cent of homes having the potential, followed by Milton Keynes and Telford and Wrekin, both at 94 per cent.
Tim Bannister, director of property data at Rightmove, said: “It’s early days, with some lenders now starting to introduce green mortgages as incentives, but homeowners need to be better informed that how green their home is will become increasingly important as we aim to move towards a net zero society, and they need more help to understand why making improvements are so important for the long-term.”