A botched net zero scheme which has caused damp issues in thousands of homes was the result of ”serious failings at every level”, a UK government official has said.

Last month, the National Audit Office found that 98% of the 23,000 homes that had external wall insulation installed under two separate schemes will result in damp and mould if left unaddressed.

Its damning report also found that hundreds of homeowners’ health and safety had been put at immediate risk because the insulation work had not been done correctly.

Appearing before Parliament, Jeremy Pocklington, the most senior civil servant at the Department for Energy Security and Net Zero, said the failures were “unacceptable”.

These schemes commonly used external wall insulation, which involved fixing insulation boards to the exterior brickwork and then applying render to make it waterproof. It can go wrong when water becomes trapped behind the boards.

The damage also applies to about a third of homes which had internal insulation installed under the ECO4 scheme and the Great British Insulation Scheme, available to residents in England, Scotland and Wales.

More than three million homes have been insulated under a variety of government schemes over the last 20 years. Billions of pounds of public money have been spent on it.

Appearing before the Public Accounts Committee, Mr Pocklington began his evidence session by saying his thoughts were with the families and households affected.

The chair of the Public Accounts Committee, Sir Geoffrey Clifton-Brown MP, said the NAO report findings were the ”worst” he’d seen in 12 years of chairing the committee and accused the department of negligence.

Mr Pocklington said there had been poor oversight of the ECO4 and the Great British Insulation Scheme by Trustmark, the body responsible for overseeing the quality of the insulation work.

However, he added that the department ”did not oversee these schemes in the way that they should have done”.

Independent MP Rupert Lowe said this amounted to ”systemic failure of a government department”.

Acknowledging this remark, Mr Pocklington, said ”there are serious failings at every level of the system that are systemic”, and that the department “didn’t take enough steps to ensure that Trustmark was set up to deliver appropriately”.

Simon Ayers, the chief executive of Trustmark, earlier told the panel of MPs that his organisation had raised the issue of faulty installations with the Department for Energy Security and Net Zero from late-2022, but they were “informal operational meetings” and minutes were not taken.

Mr Pocklington explained that the department had been under pressure after dealing with the Covid pandemic and the effect on energy prices of the war in Ukraine.

Labour MP Clive Betts asked Mr Pocklington whether the department would take responsibility for all of the homeowners that have been ”badly treated” under all of the government’s energy efficiency schemes, not just those carried out since 2022.

Mr Pocklington said the focus was on the two schemes which had taken place since 2022.

Asked by Mr Betts if the government would “stand behind” affected homeowners, Mr Pocklington said the government’s responsibility was ”to ensure that the schemes we put in place operate effectively and that there are appropriate systems of consumer protection in place”.