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 has concluded.
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 the fracking 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.
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."
It comes as protesters from environmental campaign group Frack Off brought a halt to work at a controversial gas exploration site.
They entered the shale gas rig at Banks, near Southport, Merseyside, at around 5.30am.