A controversial "fracking" technique to extract gas from the ground was the "highly probable" cause of earth tremors which hit Lancashire's Fylde coast earlier this year, a report concluded today.
One tremor of magnitude 2.3 on the Richter scale hit the area on April 1 followed by a second of magnitude 1.4 on May 27, prompting locals and environmental campaigners to blame thefracking technique being used locally by oil and gas firm Cuadrilla.
Fracking involves extracting gas reserves from underground by a process of hydraulic fracturing of shale rock using high pressure liquid to release gas - a process green groups claims is damaging the environment.
The firm commissioned a report by independent experts to investigate any links between the tremors and fracking work at their Preese Hall-1 well in Lancashire.
Today a summary published by the company said it is probable the fracking caused the tremors.
It said: "The report concludes that it is highly probable that the fracking at Preese Hall-1 well triggered the recorded seismic events.
"This was due to an unusual combination of factors including the specific geology of the well site, coupled with the pressure exerted by water injection.
"This combination of geological factors was rare and would be unlikely to occur together again at future well sites.
"If these factors were to combine again in the future, local geology limits seismic events to around magnitude 3 on the Richter scale as a worst-case scenario."
The report said a "number of factors coincided to cause the seismic events".
First, the gas well encountered a "pre-existing critically stressed fault" which "accepted large quantities of fluid", and the fault was "brittle enough to fail seismically".
The two tremors were "most likely" induced by "repeated direct injection of fluid into the same fault zone", the report states.
But it goes on to say the probability of a repeat occurrence of a "fracture-induced seismic event" with similar magnitude is "very low".
The report was published at 9am today, hours after protesters stormed the firm's gas exploration site.
Environmental campaign group Frack Off entered the shale gas rig at Banks, near Southport, at around 5.30am.
The report, titled Geo-mechanical Study Of Bowland Shale Seismicity, was commissioned by Cuadrilla Resources and carried out by a team of independent experts from across Europe, according to the company.
The report goes on to say the water-injection fracking technique is used more than 3km (about two miles) below ground and this "significantly reduces the likelihood of a seismic event of magnitude 3 or less on the Richter scale having any impact at all at the surface".
The theoretical maximum seismic event of magnitude 3 would not present a risk to personal safety or damage to property on the surface, the report states.
It proposes an "early detection system" to monitor seismic activity at Cuadrilla's drilling site which would "build in an extra layer of safety".
It proposes steps to reduce the chance of further tremors "exceeding safe limits".
Fracking has also been blamed on spoiling water supplies by fluid used in the process seeping into underground waterways.
The report states fracking carried out by Cuadrilla in the Bowland basin occurs at a depth of around 3km, whereas groundwater aquifers do not exist beyond a depth of around 300 metres (1,000 feet).
The Frack Off protest at Cuadrilla's drilling site was timed to "highlight the hypocrisy" of the Shale Gas Environmental Summit in London today.
The campaign group said the event, sponsored by companies involved in the oil and gas industry, will try to promote rapid expansion into the untapped fossil fuel.
Campaigners are also expected to stage a "Frack Mob" mass event outside the summit at 3pm.
At the drill site in Lancashire six protesters climbed up the rig to erect a banner before police were called.
A spokeswoman for Lancashire Police said: "At around 5.30am around seven protesters gained entry to the Cuadrilla gas drilling site in Banks.
"Six out of the seven have climbed up a rig on the site and have erected a banner.
"One protester remains on the ground. Police are in attendance and a cordon has been put in place around the site. We are liaising with the site owners and the protesters to bring about a peaceful resolution."
A spokesman for the company said they were assessing the situation and police had sealed off the rig.
Frack Off spokeswoman Jenny Boykin said: "Fracking uses huge amounts of water mixed with toxic chemicals, a large fraction of which are never recovered.
"The fracking fluid also leaches chemicals like arsenic out of the rocks when it is used, making it even more toxic, and so the fluid that is recovered becomes a big disposal problem.
"The contamination of irrigation water means that everyone's food supplies could potentially be affected. Fracking in the United States has already resulted in numerous spills of these fluids."
A spokesman from the Department of Energy and Climate Change said: "Cuadrilla's geomechanical study was given to the Department of Energy and Climate Change today.
"The implications of this report will be reviewed very carefully - in consultation with the British Geological Survey, independent experts, and the other key regulators, HSE and theEnvironment Agency - before any decision on the resumption of these hydraulic fracture operations is made."
In the wake of the report, Nick Molho, head of energy policy at environmental charity WWF-UK, said the findings were likely to add to the "very real concerns" people had about frackingand shale gas.
"More to the point though, we're extremely concerned by the way in which shale gas is being painted as a 'wonder gas' which will slash energy bills in Britain and help tackle climate change," he said.
"Shale gas is still a fossil fuel, and a new dash for gas could see global temperatures skyrocket.
"There's also no evidence that it will have a big impact on energy bills, which have in fact been driven up in recent years by a rising gas price.
"Our research shows that renewables are the best way of reducing our disproportionate vulnerability to the gas price and tackling climate change in the long term; the Government has to listen and resist the siren calls of the fossil fuel industry."
Last week Energy Secretary Chris Huhne warned against listening to "climate sceptics" who were suggesting that shale gas was the UK's saviour and said use of the unconventional gas source in the UK was unproved, and at best years away.
He criticised those who wanted to rely solely on shale gas to solve the UK's energy issues, and said that, while the power source was exciting, not enough was known about it to "bet the farm on it".
Friends of the Earth's senior climate campaigner Tony Bosworth said: "This report shows fracking for shale gas caused earth tremors in Lancashire - experience in the US shows it could also pollute air and water supplies.
"Extracting shale gas would suck vital funding away from clean and safe energy alternatives that could create thousands more UK jobs.
"An early seismic detection system won't be enough to make local people feel safe - there should be no more fracking in Britain until the health and environmental impacts are fully understood."
Doug Parr, chief scientist at Greenpeace, said: "Anyone who believes shale gas is the solution to our energy needs is being hopelessly naive.
"There are significant unknowns about the local and global impacts of fracking, illustrated by the conclusion by seismologists that recent fracking in the North West was responsible for a minor earthquake.
"The fact is that fracking is a distraction from the real challenges faced today in delivering clean energy at affordable prices.
"The real energy solutions of the next decade will be found in utilising the abundance of clean renewable energy sources we have in abundance.
"Drilling hundreds of metres underground, pumping high pressurised water through bore holes that may well produce limited and expensive gas supplies is a poor basis for an energy strategy."
Shadow energy minister Tom Greatrex said the report highlighted the need for a cautious approach to shale gas.
"It is welcome that the report concludes that another similar incident is unlikely to happen again, but it is important for the Government to respond fully to ensure that the correct protection regime is in place if we are to move forward with shale gas production.
"There is real potential in the shale gas reserves which have been discovered in the UK over the past few years - and work is ongoing to properly assess the scale of these reserves.
"People must have the confidence that whilst the discovery of shale gas may bring many benefits, real concerns about its exploration and production need to be addressed properly by the Government."
Mark Miller, chief executive officer of Cuadrilla Resources, said: "We unequivocally accept the findings of the independent report and we are pleased that there is no threat to people or property in the local area from our operations.
"We are ready to put in place the early detection system that has been proposed in the report so that we can provide additional confidence and security to the local community.
"Cuadrilla is working with the local and national authorities to implement the report's recommendations so we may resume our operations."