The National Audit Office published a value for money report on 14 October 2025 examining quality failures and suspected fraud in home energy efficiency installations funded through the Energy Company Obligation and the Great British Insulation Scheme1. The report covers the two current ECO schemes: ECO4, which runs from April 2022 to March 2026, and GBIS, which has broader eligibility and runs from March 2023 to March 20261.
Ofgem reports that 243,900 homes have been upgraded under ECO4 to the end of March 2025, and 60,600 homes under GBIS1. Across both schemes combined there have been 28,000 installations of external wall insulation, 3% of all measures installed, and 45,200 installations of internal wall insulation, 5%1. The government expects the schemes together to deliver £280 million in annual energy bill savings for households1.
During 2024, TrustMark, a private not-for-profit company acting as a government-endorsed quality scheme for energy efficiency retrofits, informed the Department for Energy Security and Net Zero of two separate issues1. In April 2024 it notified DESNZ of suspected fraud, whereby some retrofit businesses were overclaiming for work undertaken1. In October 2024 it notified DESNZ of high levels of external wall insulation installations that were non-compliant with the relevant quality standard, and the following month it highlighted issues with internal wall insulation1. Non-compliance covers a wide range of severity, from major issues that pose immediate risks to the health and safety of the household to minor issues such as missing paperwork1.
The NAO concluded that there have been clear failures in the design and set-up of ECO4 and GBIS and their consumer protection and quality assurance system1.
"When DESNZ and Ofgem became aware of these issues, they responded quickly. DESNZ has also been very keen to identify what went wrong, to learn lessons and to understand how to improve the system."
The report is based primarily on information held by DESNZ and Ofgem, which the NAO audits, with support from TrustMark and UKAS, which the NAO does not audit as private sector companies1. The NAO has not undertaken its own inspection of the homes affected, nor gathered evidence directly from affected households or retrofit businesses1. It does not evaluate the overall value for money of ECO or whether it is likely to achieve the expected reductions in consumer bills or carbon emissions, and does not comment on ongoing investigations into suspected fraud1.
| Measure | Installations | Share of all measures |
|---|---|---|
| External wall insulation | 28,000 | 3% |
| Internal wall insulation | 45,200 | 5% |
Why it matters for households
The schemes are intended to tackle fuel poverty and reduce carbon emissions in Great Britain by obligating energy suppliers to fund the installation of measures such as insulation in homes1. For a household that has had wall insulation installed under either scheme, the report identifies that non-compliance ranges from missing paperwork to issues posing immediate risks to health and safety1. Undetected fraud means fewer consumers may benefit overall1. The NAO states that the two challenges DESNZ now faces are ensuring the relevant businesses meet their obligations to remediate all affected homes as quickly as possible, and reforming the system so that this cannot happen again1. The report does not set out how many homes require remediation, and that figure has not been reported1.
What happens next
Both ECO4 and GBIS run to March 20261. The NAO states that DESNZ must ensure the relevant businesses remediate all affected homes as quickly as possible and reform the system so that this cannot happen again1. The report does not comment on ongoing investigations into suspected fraud1.