The consumer body selected 12 homeowners across the UK and booked EPC assessments between February and March to probe the accuracy of these tests, which were first introduced in 2007 to compare the energy efficiency of homes for buyers and renters.

The properties tested were built between 1650 and 1999 and ranged from a one-bedroom flat to a five-bedroom detached house.

The body says the results “uncovered issues with the accuracy of the results and the recommendations that homeowners received”.

In one case, a homeowner had their EPC survey done, but never received their certificate.

The survey fee was refunded, but the homeowner never learned about their home’s energy efficiency.

Of the remaining 11 participants, just one was ‘very satisfied’ with their EPC and only three said they were likely to recommend getting an EPC, based on this experience.

Most participants — eight out of 11 – complained that their EPC did not appear to be accurate, adding that descriptions of key aspects of their home like the windows, roofs and heating systems were incorrect.

Its report says: “Several participants also felt that the recommendations suggested were unaffordable.”

The study highlighted Megan Dobney’s case who achieved a D rating for energy efficiency for her two-bedroom Victorian terraced house in London.

Her EPC recommended several improvements, including internal or external wall insulation (typically costing £4,000 to £14,000 and saving £172 a year), suspended floor insulation (typically costing £800 to £1,200 and saving £70 a year,) solar water heating (typically costing £4,000 to £6,000 and saving £57 annually) and solar panels (typically costing £3,500 to £5,500 and saving £621 a year).

The report pointed out that installing all four could cost Dobney up to £26,700 and she would only see the property rise by one band from D to C.

She could save around £920 a year by installing all these energy efficiency measures – meaning it could take up to 29 years to recover the cost.

Dobney says: “The recommended changes are extremely expensive, generally for small savings each year, and would require massive disruption.”

Which? director of policy and advocacy Rocio Concha adds: “Our research shows they are in desperate need of reform — with current certificates often inaccurate and only suggesting costly improvements with long payback periods.

“The next government must make EPCs a more reliable and useful tool for householders.

“This should include reviewing the auditing and training requirements for domestic energy assessors and ensuring EPCs provide relevant information and clear, actionable advice for consumers.”

Propertymark head of policy and campaigns Timothy Douglas says: “Propertymark has long said that EPCs could be better utilised through the introduction of a property passport to increase the uptake of energy efficiency improvements.

“This would enable information to be transferable across building owners and help maintain a long-term decarbonisation goal for the building.

“The process would not replace EPCs, but enhance them, creating an opportunity to capture EPC data digitally and add to it with other data over time.

“A property passport would also provide detailed guidance on the actions required, and already undertaken, to improve the property, based on building fabric and operational data helping building owners and occupiers make decisions to improve the energy efficiency of buildings.”

Last September, Prime Minister Rishi Sunak rolled back a range of green targets, that included landlords upgrading homes to a minimum EPC rating of C, as well as delaying a ban on the sales of new petrol cars and phasing out gas boilers.

However, he said the country would still be on target to hit its 2050 net zero commitments.