The Department for Energy Security and Net Zero published its final stage impact assessment on 7 April 2025, setting out changes to the Great British Insulation Scheme (GBIS) and the Energy Company Obligation 4 (ECO4)1. The changes follow a public consultation held in November 2024, which received 122 responses1. The government response confirms three main measures: allowing two measures out of floor, loft and cavity wall insulation to be installed simultaneously as part of a GBIS project; allowing smart thermostats to be installed in the low-income group; and allowing delivery achieved under ECO4 rules to count towards an obligated supplier's GBIS target1.
The assessment states that the changes are intended to make it easier for energy suppliers to meet their obligation, which should reduce costs and increase the volume of contracts available in the market1. The original GBIS policy did not allow multiple measures to be installed in one household, only a single measure1. It also did not allow smart thermostats in the low-income group, and ECO4 annual bill savings previously had no contribution towards the GBIS annual bill savings target1.
"The changes being implemented through this government response would help to ensure ECO4 and GBIS support our statutory objectives"
GBIS was estimated to be a £1 billion obligation on energy suppliers, covering EPC D to G properties across a low-income group and a general group between Spring 2023 and March 20261. The scheme originally aimed to deliver 55,998,000 in annual bill savings1. Delivery figures from the Household Energy Efficiency National Statistics as at the end of December 2024 show 46,887 homes treated and 58,975 measures installed1.
| Metric | Count |
|---|---|
| Total number of homes | 46,887 |
| Low-income group | 17,111 |
| General group | 29,579 |
| Total number of measures | 58,975 |
| Loft insulation | 16,295 |
| Cavity wall insulation | 24,778 |
| Under floor insulation | 144 |
| Solid wall insulation | 3,254 |
| Heating controls | 12,093 |
The assessment reports that GBIS is proving more difficult and costly to deliver than originally estimated, with Ofgem reporting installation rates lower than expected and suppliers reporting higher costs and supply chain constraints1. The average GBIS cost is reported by suppliers to be £26.03 per annual bill saving, higher than assumed in the original impact assessment1. The government intends to legislate so the changes are allowed from the date of the consultation publication, 14 November 20241. The preferred option will be given effect via secondary legislation, due to be laid in May and come into force from July 20251.
Why it matters for households
The changes affect what can be installed under GBIS and ECO4 and how suppliers can meet their targets. Allowing two insulation measures per project means a household could receive loft and cavity wall insulation together, rather than one measure only1. The addition of smart thermostats in the low-income group broadens the range of measures available1. For a home's energy independence, the practical effect is that more insulation measures may be installed in a single project, which the assessment says spreads fixed compliance costs over more measures and reduces the cost of delivering annual bill savings1. The assessment notes that loft and cavity wall insulation are the most popular and cost-effective measures in GBIS, and installing both where possible results in better outcomes for installers and householders1.
The assessment states that the changes should enable obligated suppliers to meet their GBIS obligation within the original total scheme cost of £1 billion1. It also notes that the constrained supply chain, competition from ECO4, and difficulties contracting for projects in the general group have affected delivery1. The assessment says that with only a year until the end of the schemes, radical changes cannot be achieved1.
What happens next
Secondary legislation is due to be laid in May and come into force from July 20251. GBIS and ECO4 are due to end on 31 March 20261. The assessment states that the increase in delivery will be measured by Ofgem, the scheme administrators1.