Campaigners accuse the government of sitting on a potentially explosive report from its official advisers on the impact of fracking for shale gas

Pressure is growing on the UK government to release a report into the impacts of shale gas fracking, which campaigners have accused ministers of suppressing.

The Committee on Climate Change, which advises parliament on meeting the UK’s carbon targets, submitted the report in March. It covers the expected impact of exploiting the UK’s onshore oil and gas resources on nationally set greenhouse gas targets.

It can only be published when the secretary of state for energy has responded.

Green activists suspect that ministers are wary of the potentially explosive impact of the report, which is likely to find that fracking would be an addition to the UK’s carbon dioxide output, if pursued to the extent that ministers support. As well as being a wholly untapped new source of fossil fuel, and thus carbon, fracking has also been found to release more carbon than conventional oil and gas exploration, because of the difficulty of production and the dangers of leakage.

“The government is trying to start a whole new fossil fuel industry and is sitting on a report from its official advisers about the impact,” said Tony Bosworth, campaigner at Friends of the Earth. “It must publish as soon as possible, and certainly before any decision about fracking in Lancashire. If it doesn’t, the suspicions that it is trying to keep the report quiet will continue.”

If the report suggests that fracking could endanger the UK’s climate targets, it would be a key weapon for anti-fracking campaigners in their fight against the granting of planning permission for shale gas and oil works. A legal challenge being consideredagainst North Yorkshire council’s decision to allow fracking in Ryedale is based on claims that it has not adequately considered the climate impact of the technology.

All findings by the Committee on Climate Change carry significant weight as it was set up under the Climate Change Act as a statutory adviser to government.

The report is likely to recommend that the fracking industry follow strict guidelines to minimise leakage of methane, a powerful greenhouse gas.

The fracking report was mandated under the Infrastructure Act 2015, which required advice to the secretary of state by April 1 this year. After that, “as soon as is practicable” according to the act, it should be laid before parliament with an official response from the Department of Energy and Climate Change (Decc).

Originally, the committee said it expected a government response in May, allowing for a period of purdah during the local government elections on 5 May. On 11 May, the committee issued a further short statement repeating the legal position that publication must follow “as soon as is practicable”.

Pressure has been growing as the delay has lengthened. Letter-writers to the Guardian have called for publication, and a petition by pressure group 38 Degrees has more than 124,000 signatures.

Robin Russell-Jones, a long-time environmental activist who submitted scientific research to the report showing that methane emissions from fracking were worse than those of coal and that methane was rising because of fracking, wrote to the Guardian: “It would be highly embarrassing for the government if its dash for gas was found to be incompatible with our climate change commitments, agreed by the UN. Embarrassing unless the government accepted the scientific case and announced it was going to abandon fracking and invest in renewables.”

Green campaigners told the Guardian that further delay was indefensible.

“When it comes to fracking this government is about as transparent as a brick wall with no windows,” said Daisy Sands, head of energy at Greenpeace UK. “The impact of fracking on climate change is a major concern for many people. The prime minister who once promised ‘a revolution in transparency’ should release this report and give people a chance to make up their own minds.”

Vanessa Vine, of Frack-Free Sussex, who helped to organise protests against oil exploration in Balcombe, said: “It speaks volumes that this report is being withheld.”

A spokesperson for Decc said: “The Infrastructure Act clearly requires Government to consider the CCC report properly before responding, and that is what is happening. As such, if we had laid the CCC’s report before parliament as soon as we received it we would not have met our legal requirements. We are carefully looking at this report to ensure it is given the proper consideration it is due. It will be published as soon as that process is complete.”