Image copyright Getty Images Image caption Fracking has been blamed for the pollution of water supplies and causing minor earthquakes

The chairman of the Environment Agency, Lord Smith, has given his support to the expansion of the controversial "fracking" method of extracting natural gas from shale rock in the UK.

Energy companies say the use of fracking will lead to cheaper supplies.

Lord Smith told the BBC it could be a "useful addition" to the UK's "energy mix" if certain requirements were met.

But critics say there are risks from the process, which has been linked to two earth tremors in Lancashire.

Lord Smith will present his views in a lecture to the Royal Society for the encouragement of Arts, Manufactures and Commerce on Tuesday evening (which can be viewed live from 1800 BST)

The process of fracking (hydraulic fracturing) involves pumping water and chemicals into shale rock at high pressure to extract gas.

There has been a boom in the process worldwide, as nations seek new and less expensive ways to increase their energy supplies.

And last month a government-named panel of experts produced a report that said fracking should continue, but under strict conditions.

But fracking has been blamed for the pollution of underground and surface water supplies, as well as causing minor earthquakes.

Lord Smith told BBC Radio 4's Today programme that he would not stand in the way of fracking in the UK, as long as certain requirements were met, arguing that "it could be part of the answer" to the UK's energy demands.

"The source of a domestically available gas supply would, of course, be potentially very beneficial for our energy needs. It could provide energy security, which we don't necessarily have when we import gas from abroad. It could be affordable," he said.

Image caption Lord Smith is expected to say that the environmental risks of fracking may be overcome

The former Labour cabinet minister said the process was capable of causing environmental risks, but with careful monitoring these may be overcome.

Lord Smith said natural gas "has to be drawn out of the ground effectively and safely".

He said that "means worrying about the way in which the drilling takes places, it means worrying about making sure the methane is captured rather than discharged to the air and it means making sure that none of the contaminated water gets into the ground water that sometimes can fill our water supplies".

The process would have to be monitored and regulated "very rigorously", he said.

"We need to do all the tests. We need to be very careful about how we do them. My expectation is that they will be able to do them safely and, if they can, then it would provide a useful addition to our energy mix," he said.

Lord Smith also highlighted concerns about power firms capturing carbon emissions to prevent them contributing to climate change.

Climate change 'realist'

"Whilst gas is better than coal in terms of its impact on greenhouse gases and climate change, nonetheless it's still a carbon intensive fuel," he said.

He added that there was a need to for "carbon capture in storage for gas-fired power stations" to ensure that the carbon is not released into the atmosphere.

He concluded that fracking "has to be done safely and we have to develop carbon capture in the storage to enable us to reduce the greenhouse gas impact that it will have".

The Environment Agency chairman also gave his backing to nuclear power, saying "it has to be part of the overall landscape of the provision of energy".

Admitting that he had changed his mind on the issue, he told the BBC: "Twenty years ago I would have said 'over my dead body' for nuclear power.

"Now climate change has made a realist of many of us and I have to say it has to be part of the mix."

But Tony Bosworth, of the campaign group Friends of the Earth, underlined the environmental impacts of fracking and called for the technology to be "shelved in the UK as it has been elsewhere in the world" - at least until it was "proven to be safe".

"We know 85% of people want to see more clean British energy, not gas", he said, arguing that ministers should focus less time and money on technologies that are unproven or, "like nuclear, are consistently late and reliant on vast public subsidies".

"The Government's plans for the electricity market must ensure that renewable energy fills the gap caused by the closure of power stations and the collapse of nuclear investment - this will boost our economy by creating thousands of new jobs."

Fracking is currently prohibited in France and Bulgaria, while US state Vermont has also approved an outright ban.