Protests, legal challenges and planning rejections have failed to stop the return of fracking in Britain, but the government’s regulations on earthquakes are fast emerging as the biggest threat to the nascent shale gas industry.

The energy company Cuadrilla has been forced to stop work at its Preston New Road site in Lancashire twice in four days – on Friday last week and on Monday – due to minor earthquakes occurring while it was fracking. The tremors breached a seismic threshold imposed after fracking caused minor earthquakes at a nearby Cuadrilla site in 2011.

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Francis Egan, the firm’s chief executive, told the Guardian on Monday that the limits were proving “extremely challenging” and it was time they were reconsidered. But the energy minister, Claire Perry, rejected that call, saying it would be “a very foolish politician” who relaxed standards “when we we are trying to reassure people about safety”.

Fracking firms must temporarily halt operations if a quake is triggered above 0.5-magnitude – far below anything that could be felt at the surface. If a 0.5-magnitude tremor occurred at surface-level, it would be akin to the vibrations of a passing car.

Q&A What is fracking? Show Hide Fracking, or hydraulic fracturing, is a way of extracting natural gas from shale rock formations that are often deep underground. It involves pumping water, chemicals and usually sand underground at high pressure to fracture shale – hence the name – and release the gas trapped within to be collected back at the surface. The technology has transformed the US energy landscape in the last decade, owing to the combination of high-volume fracking – 1.5m gallons of water per well, on average – and the relatively modern ability to drill horizontally into shale after a vertical well has been drilled. In England, the government placed a moratorium on fracking in November 2019 after protests, legal challenges and planning rejections. A year earlier, the energy company Cuadrilla was forced to stop work at its Preston New Road site in Lancashire twice in four days due to minor earthquakes occurring while it was fracking. The tremors breached a seismic threshold imposed after fracking caused minor earthquakes at a nearby Cuadrilla site in 2011. In March 2019 the high court ruled that the government's fracking guidelines were unlawful because they had failed to sufficiently consider scientific evidence against fracking.

The architects of the regulations are split on whether there should be a rethink. Peter Styles, one of the geologists who set the threshold, said: “We have started this frack now. If we stop now, we will never learn what happens in the UK situation. My opinion is for better or for worse they’re [Cuadrilla] going to have to tough it out unless we get earthquakes that are significant enough to be disruptive.”

Styles, professor emeritus in applied and environmental geophysics at Keele University, said it was right the government rejected calls by Egan to lift the limit.

“They [Cuadrilla] don’t like it because it costs them money when they stop, but that’s part of this game. It’s not the time to raise it. Let’s carry it out under these rules, observe it, and then revisit it when we have the data.”

However, Dr Brian Baptie, a seismologist at the British Geological Survey who also drew up the rules, said there was a risk the threshold was so low it could make fracking economically unviable.

“By having this very conservative seismic threshold, putting the risk at an extremely cautious level, then that might have a knock-on effect for the whole operation. Which I think would be wrong [from a scientific point of view],” he said.

The Guardian revealed recently thatPerry had privately said she would consider relaxing the seismic threshold as the industry grows and learns more about the process. But Perry and other ministers subsequently insisted no such plans existed.

Styles, who met with Perry on Wednesday to discuss fracking-induced tremors, said: “Politically, it’s quite difficult to change it.”

Stuart Haszeldine, professor of geology at the University of Edinburgh, said the government had set itself a trap with the regulations, which he felt could safely be raised if the monitoring regime was made more open.

“This is a really difficult box to get out of now. If they increase the limit from 0.5 up to 1.0, clearly they’ll be open to accusations of connivance with the industry,” he said.

Asked whether 0.5 was the right number, he said: “In terms of perception it’s a great number. In terms of science it’s not particularly rational. In terms of trying to enable the drilling to occur it’s too stringent.”

Cuadrilla has said every day of delay costs it £94,000, so the stop-start nature of fracking due to the regulations could wreck the economics of UK shale gas.

“It’s going to make drilling for shale gas in Lancashire perhaps double the cost of what was originally anticipated,” said Haszeldine.

Egan said the rules should be relaxed. “The authors of the report upon which the current seismic traffic light system is based were clear that the threshold value of 0.5-magnitude could be adjusted upwards over time.

“It may well be that we have reached that time not only for the UK shale gas industry, but also to address the concerns of local people who are becoming increasingly worried by reporting of tiny movements in the Earth which occur thousands of times across the UK every day as if they were harmful earthquakes.”

Facebook Twitter Pinterest Anti-fracking protest in Blackpool on October 20 2018. Photograph: Rod Harbinson/ZUMA Wire/REX/Shutterstock

He added that it was impossible to frack without creating mini earthquakes deep underground, and compared the company’s operations to a major construction project such as Crossrail, the underground rail service in central London, which he said could not be done “without causing similar or greater levels of induced ground movements”.

The threshold was set at 0.5-magnitude in 2012, with the rationale that earthquakes triggered after fracking operations could be as much as 1 magnitude higher than those during fracking. That would result in 1.5-magnitude tremors, the same level as one of the quakes in 2011 when Cuadrilla fracked at its Preese Hall site in Lancashire. Cuadrilla did not challenge the limits when they were established six years ago.

As the company and geologists have pointed out, the limits are far lower than in other countries. In the Canadian provinces of British Columbia and Alberta, fracking operations are only halted in the event of 4-magnitude quakes.

Increasingly, it looks like the UK government’s fracking aspirations could be dashed by its own rules.