The debate in the UK over the pros and cons of exploiting reserves of shale gas heightened in August after prime minister David Cameron said that he was "determined" to see projects go ahead.

Writing in the national press, Cameron said that shale gas exploration and ‘fracking’ – the controversial gas extraction technique – would drive down energy bills, create jobs and boost investment.

His comments drew criticism from conservation and environmental groups, which in response wrote an open letter to Cameron calling for the government to "put the brakes on fracking".

The debate has been thrown into sharp focus as Cuadrilla, the oil and gas firm that has been exploring for shale gas in north-west England, started operations at an exploratory onshore oil well in Balcombe, south-east England.

Protesters gathered at the Balcombe site to show their opposition to fracking and eventually caused Cuadrilla to scale back its operations at the site because of concerns over safety.

The latest estimates indicate that there are at least 1300 trillion cubic feet of shale gas lying underneath Britain. "To put that in context, even if we extract just a tenth of that figure, that is still the equivalent of 51 years’ gas supply," said Cameron, who used the example of the USA to show the impact that shale gas could have on the economy.

Environmentalists, however, believe that fracking – which involves pumping water, sand and chemicals into the ground at high pressure to release gas – poses a threat to communities and the environment.

"If we embrace fracking to the degree proposed by the coalition [government], the UK will be left with a gas-dependent energy system for decades to come, meaning our ability to meet our legally-binding carbon targets will be significantly compromised," said the group of conservation and environmental NGOs – including WWF and Greenpeace – in their letter.

"Meanwhile there is no evidence that UK shale will reduce household energy bills and the clean technologies that can actually limit climate impacts, improve energy efficiency and deliver cheaper energy over time are being side-lined."

The oil and gas sector has defended Cuadrilla’s operations at Balcombe, with the UK Onshore Operators’ Group (UKOOG) pointing out in an open letter that the exploratory well at Balcombe is a conventional oil exploration site rather than a fracking site. "The UK has benefited from having an onshore oil and gas industry for over a century. Over 2000 wells have been drilled – many of them hydraulically fractured – and over 300 are currently operational," said Ken Cronin, CEO of UKOOG.