The huge scale of a natural gas field discovered under the north-west of England has been revealed, potentially revolutionising the UK's energy outlook and creating thousands of jobs, but environmental groups are alarmed at the controversial method by which the gas is extracted.

Preliminary wells drilled around Blackpool have uncovered 5.6tn cubic metres (200tn cubic ft) – equal to the kind of recoverable reserves of big energy exporting countries such as Venezuela, according to Cuadrilla Resources, a small energy company which has the former BP boss Lord Browne on its board. It said up to 800 more wells might be drilled in the region, creating 5,600 jobs and promising a repeat of the "shale gas revolution" that swept the US, sending local energy prices spinning downwards.

Even if only a relatively small fraction of gas could be exploited, it could trigger a rush of drilling in other parts of the UK at a time when Britain is running out of North Sea reserves.

But Cuadrilla's extravagant claims have alarmed environmentalists and unnerved supporters of wind power. Green groups are opposed to the hydraulic fracturing – "fracking" – process by which the gas is unlocked from shale rock, pointing out it remains banned in parts of the US and France over fears that water aquifers could be contaminated.

The process involves drilling a well then pumping in millions of gallons of water, sand and chemicals under high pressure. The pressure fractures underground shale deposits and opens fissures that enable natural gas to flow more freely out of the well. For each frack, 80-300 tonnes of chemicals may be used, critics claim.

The natural gas industry does not have to disclose the chemicals used, but scientists have identified volatile organic compounds such as toluene, ethylbenzene, xylene and benzene, the latter of which is a strong carcinogen.

A 2010 US documentary film, Gasland, showed homeowners setting fire to the water coming out of their taps, such was the volume of methane contained in the water. The flames were said to be the result of nearby fracking operations contaminating the water supply, but the oil industry has denied this.

Mark Miller, chief executive of Cuadrilla, said he was enormously encouraged by the potential of the Lancashire region, which appeared to have the same potential as the best shale gas producing areas in Texas. He said it was not possible to say what the exact amount of recoverable reserves would be without further drilling and he admitted 200tn cubic feet was a very large number

"Typical extraction rates in the US on a well by well basis would be between 10% and 30% [of the reserves in place] but it all depends on the number of wells we drill," he added. About 400 wells could be expected as a conservative estimate, he said, with up to 800 in the licence area between Blackpool and Southport over the next 15 years.

Cuadrilla, which used the fracking process five times on the first well but has since stopped, said it was drawing up a plan to be handed over to Department of Energy and Climate Change shortly. "We won't carry forward [any further fracking] till DECC has seen the report and is happy about public safety," said Miller.

The shale gas finds are largely due to new technology being used to produce the wells, and oil companies are busy looking for new discoveries in places as far afield as Poland and China.

Shale gas represents a potential problem for governments trying to reduce CO 2 emissions, as there are significant emissions when it is burned. However, it is also a potentially much cheaper alternative to wind and solar power, which both currently require public subsidies.

The environmental campaign group Friends of the Earth said it remained totally opposed to any more fracking until the safety and environmental impact was fully understood. "We are also worried that a new shale gas goldmine would take money away from renewables," said a spokeswoman.

The Co-operative, which is championing renewables in its new retail energy business, also expressed concerns about the upbeat statements coming out of Cuadrilla, which is partly owned by the Australian oil services group AJ Lucas.

"On the face of it, new natural gas finds appear to be good news, but the government must not be seduced by this without considering all the impacts of shale gas extraction," said Paul Monaghan, head of social goals at the Co-operative group.

Blackpool oil shale reserves. Photograph: guardian.co.uk

"That is why we are calling for a moratorium on any further exploitation of shale gas, which will allow the wider environmental concerns to be fully exposed and addressed."