Ed Davey, the energy and climate change secretary, has warned supporters of shale gas that it may take many years for substantial exploration in the UK, and predicted it would not lead to an era of cheap gas.
Davey was speaking to the Guardian before the publication of the energy bill on Thursday and promised he had weapons he could use if there was a danger his policies were locking too much gas into the energy mix.
It is expected that the chancellor, George Osborne, will publish a strategy for gas alongside his autumn statement next week and, at the same time, Davey will give permission for the restart of suspended exploration of shale. The suspension was imposed last year due to concerns about the fracking technology used to exploit it by the company Cuadrilla.
Davey said: "I have never been anti-shale gas. I think shale gas has a real role to play, not least in energy security if we can get shale gas in an environmentally safe way and in a way that is publicly acceptable.
"The thing about shale gas is people over-promise about what it will do – they say we have got huge supplies ... but the truth is that nobody knows. Even if they can estimate the reserves in the UK, you have to lay across that what is technically recoverable and what is economically recoverable.
"I am optimistic. I hope we will be able to produce a lot, but in terms of big production of shale gas it is going to take years. It is not going to happen tomorrow. Sometimes you listen to some of the commentators and they seem to think you can just turn shale gas on."
He claimed advocates of shale gas, such as the Spectator editor, Fraser Nelson, were unrealistic about what shale might do to prices: "There are people like Fraser Nelson who think we can get cheap gas and cheap energy here only if we had shale gas tomorrow. Not only will we not get shale gas tomorrow, but it is very unclear what the impact on the gas and energy price will be.
"The ideas that we can replicate the north American experience here is really not proven. Many people have huge doubts about that even globally. It is said there is shale in Ukraine, China, Algeria and Argentina and no doubt other places, but even if we do mange to get all that, many people – gas market analysts, international energy agencies – say it is still not going to produce cheap energy."
Davey predicted "the demand effect is going to swamp the supply effect even though there is a lot of gas being found."
He said if the government was in danger of locking in too much gas, he still had the weapons available, including raising the emission performance standards of gas fired power stations.
"There is quite a lot of gas that we need even within our climate change targets so it is not like anywhere near the position that we have too much gas," he said.
"Dash for gas is an overused phrase because we do need more gas; the green groups acknowledge that we need more gas and we are some way away from thinking we have too much.
"I will be taking that decision soon about whether Cuadrilla can continue with their drilling. If we allow them to drill they will need permission before they actually produce shale gas."