The government has handed energy companies £22bn in billpayer-backed subsidies to burn wood for electricity despite being unable to prove the industry meets sustainability standards, the government’s spending watchdog has said. The head of the National Audit Office (NAO) has called on the government to rethink how it monitors compliance with its biomass sustainability regime, which has handed about £1bn a year to generators, because the assurances do not provide confidence that the environmental requirements have been met. Last week, the government put forward controversial plans to offer Britain’s biggest biomass generator, the Drax plant in North Yorkshire, extra subsidies to burn trees for electricity until the end of the decade. Biomass has provided about a 10th of UK electricity in recent years. It is considered a key plank in the government’s plan to reduce emissions from electricity to near zero by 2035. Many green campaigners, scientists and MPs are fiercely opposed to burning wood pellets that they claim damages natural ecosystems and increases carbon emissions. Gareth Davies, the 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.” Drax stands to earn an extra £2bn in subsidies under the government’s plan to extend subsidies to the power plant beyond the end of the scheme in 2027. The government has also granted permission for Drax to fit carbon capture technology to biomass plant, in a project that could cost billpayers an estimated £40bn. The government’s biomass sustainability monitoring relies on a combination industry-backed data, third-party certifications and some assurance audit reports. The NAO has suggested the government should devote more resources to ensure that energy companies are being compliant. Matt Williams, an advocate for the Natural Resources Defense Council, a US-based environmental group, said the NAO’s findings suggest “billions of billpayer cash could have been used to cause environmental damage”, adding that extending Drax’s subsidies in these circumstances was unjustifiable. Selaine Saxby, the Conservative MP for North Devon, said: “Since we first decided to subsidise energy generation from woody biomass, as part of the transition from coal, it has become clear that the science on the technology has changed. “Far more sustainable options have now been developed and improved, such as solar, wind and nuclear power generation, and I call on the government to support these technologies over biomass energy generation.” A spokesperson for the government said its sustainability criteria was in line with internationally recognised standards, and it would be consulting later this year on how the UK could go further.