Burning wood from forests for energy could be worse for the climate than coal, the government has been warned, after the practice was recommended by its net zero advisory body.
The Committee on Climate Change called for subsidies to support the expansion of forest cover across the UK as part of its plan to meet its legally binding net zero target.
It said some of the forests could be used "sustainably for combustion and carbon sequestration in the energy sector".
But Duncan Brack, a energy specialist at think tank Chatham House, said chopping down forests for renewable energy was "almost certainly counterproductive".
"Expanding forest cover is undoubtedly a good thing, if you're leaving them standing," Mr Brack, who was special adviser at the Department of Energy and Climate Change between 2010 and 2012. But he warned claims that cutting down trees to create energy was carbon neutral were "highly dubious".
Biomass production has boomed across Europe and America in recent years. Last year it provided 12 per cent of the UK's electricity, making it the second most successful source of renewable energy after wind. In 2017 the British biomass industry, which is run mostly on imported wood pellets, received £1 billion in government subsidies.
Claims that trees are a carbon neutral source of energy rely on the assumption that the emissions created when they are burned is easily matched by planting new ones. But most models do not take account of the fact older trees absorb carbon at a much greater rater, and the delay in replacing that with new forests.
"You can leave trees standing and they will continue to absorb carbon for decades," Mr Brack said. "But the biomass industry implicitly assumes that forests at some point stop reach a saturation point for carbon intake and can be harvested and simply replaced."
His views were supported by forestry NGO Fern, which said burning wood for energy on an industrial scale could be "worse for the climate than burning coal, expensive and harmful to human health".
The use of potentially carbon intensive forestry also undermines the role of biomass in creating "negative emissions", a core part of the government's plan to meet net zero by 2050.
So-called "carbon capture and storage", which does not yet exist on a large scale, uses technology to remove the emissions created from burning biomass and store them into the ground.
Fern, which is part funded by the Department for International Development, warned the government against relying on the technology, which it said was "not viable due to serious technological, economic and environmental barriers. Protecting and restoring existing forests on the other hand would be cheaper and do more for the climate. This is what the government should focus on.”
Mr Brack suggested that subsidies for the biomass industry would be better used to pay for forestry conservation, which could maximise the green potential of trees.
But he added that the use of biomass could play a vital role in renewable energy, depending on its source. The use of grassland crops and short rotation coppice, which the CCC also recommends in its report, could be a much greener alternative.
The CCC itself warned in 2018 that the government should carefully scrutinise the sources of biomass energy and avoid those that "do not sequester carbon" where there were other renewable alternatives.