The government’s fracking tsar has quit the post after just six months, claiming policy relating to the controversial process means there is “no purpose” to her job.

Natascha Engel told the business secretary, Greg Clark, that developing the industry would be “an impossible task” despite its “enormous potential”. In her resignation letter, she said environmental activists had been “highly successful” in encouraging the government to curb fracking.

Engel, a former Labour MP, wrote the letter following two weeks of protests by the Extinction Rebellion group, which brought parts of London to a standstill with demands to cut emissions to zero by 2025.

She wrote: “A perfectly viable and exciting new industry that could help meet our carbon reduction targets, make us energy secure and provide jobs in parts of the country that really need them is in danger of withering on the vine – not for any technical or safety reasons, but because of a political decision.”

Engel complained that a traffic light system that halts fracking when a tremor with a magnitude of 0.5 is recorded “amounts to a de facto ban”.

“The UK could be on the cusp of an energy revolution the like of which we have not seen since the discovery of North Sea oil and gas,” she wrote.

Protesters stand outside Cuadrilla’s Preston Road fracking site near Blackpool. Photograph: Hannah Mckay/Reuters

Fracking, she said, had the potential to create jobs, economic security and provide a cleaner alternative to coal and biomass.

Critics say the amount of water needed for fracking is damaging to the environment and claim it releases dangerous chemicals. They also say governments should focus on renewable energy.

Engel’s resignation letter said: “The UK is currently spending £7bn a year on importing gas – money that is not being used to build schools, hospitals or fix the potholes in our roads. Developing our own shale gas industry would mean money going into the Treasury rather than out.”

She added: “We know shale gas can be extracted safely. We have the best regulations and regulators in the world. We know the positive impact it has on local communities, but we are choosing to listen to a powerful environmental lobby campaigning against fracking rather than allowing science and evidence to guide our policy making.”

She said “apart from its uniquely awful name” the process is “materially no different” from other methods of hydrocarbon extraction.

“We are listening to a small but loud environmental movement that opposes in principle all extraction of fossil fuels,” Engel wrote. “The campaign against fracking has been highly successful in raising the profile and filling the coffers of some NGOs, but they do not represent local residents nor the wider population.”

In a statement following her resignation, Engel said: “I hope there will be a rethink sooner rather than later which will see policy guided by science, rather than fear-mongering.

“There is much to be optimistic about how developing technologies – including fracking – can help us accelerate the reduction in CO2 and grow our economy. Sadly today only those who shout get heard.”