The majority of new homes rely on carbon-intensive gas boilers after developers lobbied Conservative governments to water down proposed laws on cutting emissions from buildings, openDemocracy can reveal.

Two-thirds of new homes built in England in the year to the end of March 2022 use gas for central heating, according to data compiled by the Office for National Statistics following a request by openDemocracy.

Experts have warned households will face large bills to retrofit properties as a result of watered-down or delayed plans to cut greenhouse gas emissions.

Last year, Boris Johnson was persuaded to delay a ban on developers connecting new homes to the gas grid. The government had considered implementing the policy, known as the ‘Future Homes Standard’, next year but it is now due to come into force in 2025. Even then, there will be loopholes that could allow developers to continue selling new homes with gas boilers until the end of 2026.

Taylor Wimpey, one of the UK’s largest housebuilders, tried to weaken the Future Homes Standard, Greenpeace’s Unearthed unit revealed last year. The company argued that the government’s proposal to cut emissions from new homes by 75-80% compared with the existing standard was “too ambitious”.

In May, Johnson’s government rejected a recommendation by the House of Commons’ Business, Energy and Industrial Strategy (BEIS) Committee that the policy be brought forward to 2023.

Speaking to openDemocracy, Darren Jones, the committee’s chair, warned that delaying the policy would cost households thousands of pounds – and accused developers of “passing the buck onto homeowners and tenants”.

“Retrofitting leaky gas-fitted newbuilds will cost households thousands more than the cost of fitting efficient heat pumps in the first place,” Jones said.

“Whilst developers continue to line their own pockets, ordinary people are having to foot the bill. The government needs to get a move on and make low-carbon heating and energy efficiency standards mandatory.”

Retrofitting a new home to meet high energy efficiency standards – including replacing its gas boiler with a heat pump – could cost a household an average of £26,000, according to a Climate Change Committee (CCC) data.

That is over five times more than the £4,800 it would have cost to meet the standard when a property was first built.

Homes account for about 21% of UK carbon emissions. Unless the government greatly accelerates the shift from gas heating to heat pumps, it will not meet its target of net-zero emissions by 2050, the CCC has warned.

The ONS data shows developers failed to reduce the proportion of new homes being built with gas boilers last year, with the percentage remaining the same, 64%, as in the previous year.

The Home Builders Federation, which represents major housebuilders, has sought to justify the slow transition from gas boilers to heat pumps for new homes by arguing that there are problems with the supply chain and a lack of electricity capacity.

But Jan Rosenow, of the Regulatory Assistance Project, a clean energy think tank, told openDemocracy there were no valid reasons why builders in England could not follow the example of those abroad, who have already drastically reduced the use of gas boilers.

Rosenow said: “The fact that most new homes [in England] are still being connected to the gas grid is absolutely scandalous. It means additional and avoidable fossil gas use, higher emissions from buildings and compromises the UK’s ability to meet its climate goals.”

In Germany, only 16% of homes approved to be built in the first half of 2022 will have a gas boiler and in Norway, 96% of all new heating systems are now heat pumps.

Rosenow added: “Installing fossil gas boilers in new homes means we will have to go back and retrofit them with a new low-carbon heating system later. This will be unnecessarily expensive, disruptive and could be entirely avoided.”

In 2019, housebuilding firm Persimmon admitted to MPs that in 2015 it had lobbied against the ‘Zero Carbon Homes’ policy, which was eventually scrapped by then-chancellor George Osborne.

Rosenow branded Osborne’s decision “a huge mistake” that has “resulted in millions of tonnes of carbon emissions already”. He added: “It resulted in more than one million homes being built, most of which have been fitted with a fossil fuel heating system. Most of these homes will now have to be retrofitted.”

Last year Taylor Wimpey told Unearthed: “Taylor Wimpey communicated its support in the consultation response and remains fully supportive of the UK government’s target to achieve net zero emissions by 2050. We also embrace the Future Homes Standard with its ambition to reduce carbon emissions from homes in use by 75-80% by 2025.

“In response to the government’s calls for honest interaction and dialogue around the Future Homes Standard in 2020, Taylor Wimpey identified a number of challenges relating to the practical implementation of the proposals. These challenges led to concerns that the delivery of viable and much-needed new housing could be prejudiced, which we duly communicated to the government in our response.”

Neil Jefferson, managing director of the Home Builders Federation, said: “New build homes emit on average a third of the carbon of an older property, saving owners thousands of pounds in energy bills and the industry is committed to going further and meeting all the challenging environmental targets set.

“The use of heat pumps in new build homes is increasing and will become the norm over time. However, there is currently not the capacity in the supply chain to manufacture, fit and maintain systems, or in some local power networks to meet the competing demands being placed on them.”

Persimmon and the Department for Levelling Up, Housing and Communities did not respond to openDemocracy’s request for comment.