The two candidates vying to be the country’s prime minister are being urged by Frack Free Ryedale to stand by the Conservative manifesto pledge to keep a ban on fracking.

Both Liz Truss and Rishi Sunak have said that they would allow fracking if local people support it, as they seek to bolster domestic gas supplies in response to the energy crisis.

The process has been banned in England since 2019 on safety grounds after Cuadrilla caused earth tremors far stronger than it had anticipated in Lancashire.

The Tories said then that they would not “support fracking unless the science shows categorically that it can be done safely”.

In a letter to both candidates, Charles Hendry, who was energy minister in the coalition government, and organisations including the RSPB, the CPRE and the Woodland Trust, along with members of Frack Free Ryedale, urges Truss and Sunak to act “with integrity by upholding the manifesto pledge on fracking”.

Ryedale became a frontline in the battle over fracking following Third Energy’s proposals for the hydraulic fracturing of rock to extract gas in Kirby Misperton.

More than 80 protesters were arrested over the course of the campaign as they hampered the firm’s wish to be the first to frack in the UK for years.

Third Energy spent millions developing its site and hundreds of thousands of pounds from the public purse was spent policing the site before a government financial review led to test work being put on hold and ministers announcing a moratorium on fracking in 2019.

Following the Government’s decision to ban fracking, Third Energy was sold to York Energy, and Knapton power station and Knapton Energy One Limited are now run by Third Energy Trading Limited.

The company is now committed to several green energy projects that will make use of the Knapton site and removing the fossil fuel-related equipment from the past is necessary to make room for those green projects.

Fracking is deeply unpopular with the public, and has been strongly opposed by local communities everywhere it has been proposed because of concerns about earthquakes, climate change and the industrialisation of the countryside.

In April Kwasi Kwarteng, the business secretary, commissioned the British Geological Survey to review whether scientific breakthroughs had changed this, whether geology outside Lancashire might be more conducive to fracking without tremors and whether the differences between the tremors permitted by fracking and by other industries such as construction were justified.

The results of this review were handed to the Government in June but are yet to be published.

The letter to the two candidates is also signed by Nick Howard, from Castle Howard, Dr Tim Thornton, a local retired GP and several members of Frack Free Ryedale.

Campaign director of Frack Free United, Steve Mason, said: “Any threat of fracking returning to North Yorkshire is deeply concerning for communities. They have moved on, and here in Ryedale there is a focus on delivering change for the better, but, as it’s been pointed out to me by so many over the past few weeks, there is a strong resolve within the area that they will not accept a return of fracking.”

The letter to the two candidates, also signed by WWF, the Angling Trust, Unison and the End Fuel Poverty Coalition, highlights comments made by Kwarteng in February when he said that fracking would not “materially affect the wholesale market price”.

They urge the next prime minister to focus on home insulation and developing more cheap renewable power.

Danny Gross, of Friends of the Earth, said: “If the next prime minister breaks the Conservative Party’s manifesto promise by reviving fracking – which would industrialise the countryside and worsen climate breakdown – local people will once again stand against it.”