The risk that drinking water in Sussex could be contaminated by fracking chemicals was known by the Government more than a year ago, previously secret documents reveal.

Ministers were privately briefed by the Environment Agency (EA) that fracking near aquifers – underground rocks which contain water – should not be permitted.

But the EA’s head of climate change later changed the wording on a public statement related to the issue so as not to create “too stark a message” about shale gas drilling.

The revelations – which could have major implications for the future of fracking in Sussex – were made the day after Prime Minister David Cameron said residents must accept the controversial practice in their communities and dismiss safety concerns.

Mr Cameron wrote: “There is no reason why fracking should cause contamination of water supplies or other environmental damage if properly regulated.”

The EA revealed the guidance to Charles Hendry, former Energy Minister and MP for Wealden, after he asked for help responding to a correspondent’s concerns about fracking in Balcombe, West Sussex.

Residents of the village are worried Cuadrilla, which is currently testing for oil and shale gas at the site, could later switch to fracking, contaminating the water supply.

The EA yesterday told The Argus the aquifer near Balcombe is poor and not suitable for public drinking, although campaigners remain concerned about how the drill site could pollute the River Ouse, which is just half a mile away, and the nearby Ardingly reservoir.

But across Sussex, 75% of drinking water comes from these underground supplies, raising fears of widespread contamination if the county’s huge shale gas reserve is exploited.

In a private memo, revealed by Greenpeace through Freedom of Information requests to Number Ten, a senior EA official writes: “The Environment Agency would not allow hydraulic fracking to take place in an area where there are aquifers used to supply drinking water.

“If there were sensitive ground waters present in an area where a company wanted to carry out hydraulic fracturing, we would object during the company’s planning application and refuse to grant an environmental permit.”

But the guidance was not released to the public and the EA’s head of climate change suggested the wording should be changed.

Responding to Mr Hendry’s request for information, the head of climate change says the initial guidance “provided a too stark view of our position of where we would or would not be happy with shale gas developments in relation to potable ground water aquifers”.

The official adds: “Can I ask that you [Mr Hendry] do not use the two sentences from …[redacted]..... while we finesse them.”

Campaign group Frack Off estimate 6,700 drill wells would be needed to extract just 10% of the county’s shale gas reserves.

Leila Deen, of Greenpeace, said: “Water is an ongoing issue in the south, and locals would be right to be concerned about fracking companies using vast quantities of it for shale gas extraction, and the risk of contamination.

“Just this week, the Government’s former chief scientific advisor said people’s fears about contaminated water from fracking were entirely rationale.”

An Environment Agency spokesman refused to respond to claims it had water down the public statements on the dangers of fracking.

He said: “The UK regulatory regime ensures that hazardous substances must not be allowed to enter groundwater.

“A permit, under the Environmental Permitting Regulations 2010 (EPR), from the Environment Agency is required where fluids containing pollutants are injected into ground, where they may enter groundwater.

“This may also be needed if the activity poses a risk of mobilising natural substances that could then cause pollution.

“The permit will specify any necessary limits on the activity, any requirements for monitoring, the chemicals which may be used and any appropriate limits on permissible concentrations.

“If the activity poses an unacceptable risk to the environment the activity will not be permitted.”

Last night Cuadrilla bosses has said its exploration site at Balcombe in West Sussex is "unlikely" to become a full production location. They refuse to rule out fracking at the site in the future.

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