The Government cannot prove that biomass fuel is sustainably sourced and its assurance schemes are not good enough, a National Audit Office (NAO) report has found.

Ministers and their advisers at the Climate Change Committee (CCC) consider biomass to be a low-carbon source of energy if 70 per cent of it is produced following a strict set of sustainability criteria.

Generators, the largest of which in the UK is Drax, near Selby, must say where exactly the wood used for burning has come from and describe how that forest is managed.

They must submit an independently audited report each year which is reviewed by the regulator Ofgem, the purpose of which is to prove that the wood has not contributed to further deforestation and the destruction of nature.

Scientists and campaigners have said this is happening anyway and a BBC Panorama investigation last year found that biomass production was affecting ancient forests in Canada.

In its response to the NAO’s findings, the Government did not address its concerns that destructive practices may be going under the radar and instead celebrated that the NAO found no evidence of firms not complying, despite that not being the purpose of the report.

In 2021, the UK imported 9.1 million tonnes of wood pellets for energy, with 60 per cent from the US, 18 per cent from the EU and 16 per cent from Canada, the NAO said.

Figures from the following year show that biomass accounted for 11 per cent of total electricity generation, up from three per cent in 2010.

The Government has so far supported the industry with £22 billion and is considering supporting Drax beyond the current subsidy scheme deadline in 2027 to help it develop carbon capture technology at its plant in North Yorkshire.

Drax and the Government claim biomass production can be “carbon negative” in that the CO2 absorbed by the trees as they grow is burnt off but then captured and stored underground instead of returning to the atmosphere, resulting in a net reduction.

The Government and the CCC say this could help offset emissions from other sectors without any low-carbon alternative such as aviation, though some scientists have questioned whether this technology is truly feasible.

Gareth Davies, head of the NAO, said: “If biomass is going to play a key role in the transition to net zero, the Government needs to be confident that the industry is meeting high sustainability standards.

“However, Government has been unable to demonstrate its current assurances are adequate to provide confidence in this regard.

“Government must review the assurance arrangements for these schemes, including ensuring that it has provided adequate resources to give it assurance over the billions of pounds involved.”

The Department for Energy Security and Net Zero (DESNZ) has said it is considering raising the 70 per cent requirement from sustainable sources to 100 per cent.

Auditors said it should consider the risks of non-compliance and provide more resources towards monitoring for any breaches.

The NAO also wants the Government to review the way it seeks assurance that wood is sustainably sourced.

Its method uses a combination of information given by biomass energy generators, third-party certification schemes and limited-assurance audit reports.

A DESNZ spokesperson said: “We welcome the NAO’s report, which found no evidence of firms not complying with our stringent sustainability criteria, which are in line with internationally recognised standards.

“As set out in the Biomass Strategy, we will be consulting later this year on how we can go further than our peers.

“Biomass will provide a key role in a more secure, clean energy sector. It delivered around nine per cent of the UK’s total energy supply in 2022, with generators only legally receiving subsidies if they prove they have complied with our strict rules.

“The Climate Change Committee has acknowledged that achieving net zero is dependent on solutions like bioenergy with carbon capture and storage, which will help offset emissions from other industries.”