THE SNP has come under further pressure over its policy on fracking after it emerged that one of the party's candidates had previously spoken out strongly in favour of unconventional oil and gas.

George Kerevan, who is standing in East Lothian, wrote an article in 2012 in which he highlighted the benefits of the 'shale gas revolution' in the United States and said opposition to fracking by environmentalists was "based on a utopian vision rather than a problem-solving one".

However, in campaign literature for the current campaign he described himself as a "Home Rule, jobs not austerity, no fracking, no Trident, a voice for East Lothian" candidate.

Mr Kerevan's article emerged after the SNP was criticised for issuing green badges with the slogan 'Frack Off' written on alongside an SNP symbol.

While Fergus Ewing, the SNP's energy minister, called a moratorium to fracking in January, he has so far failed to answer a series of questions setting out precisely what is covered by the temporary ban, and how further research into fracking will be carried out.

Ineos, the firm which holds 729 sq miles of fracking exploration licences across central Scotland, is understood to have continued preparatory work for fracking and is apparently relaxed about the moratorium imposed by the SNP.

Scottish Labour's Candidate for East Lothian, Fiona O'Donnell, said: "George Kerevan must come clean. When he wants your vote he'll claim he is opposed, but he has been a cheerleader for fracking. Has he changed his mind, or is he someone who will say anything to get selected, and then elected?"

In a BBC documentary broadcast last night, Mr Ewing appeared to leave the door open to fracking, calling for a "national debate" over the issue and refusing to commit to a permanent ban even if a public consultation finds Scots are resolutely against it.

Mr Ewing said: "Hydraulic fracturing has been carried out in the USA on a very large scale. But the central belt of Scotland is not North Dakota. It is different and we need to think how it will be, how it may be, applied to Scotland."

The comments were criticised by Patrick Harvie, co-convenor of the Scottish Greens. He said: "I have no doubt many will be alarmed at these comments. Not only is the SNP's energy minister still talking about this dangerous industry as an opportunity, but he appears to be suggesting it will eventually take place."

The SNP accused Labour of "desperation" after highlighting Mr Kerevan's previous stance. A spokesman said: "Like many people across Scotland, George Kerevan's concern over the implications of fracking has grown as more environmental evidence has emerged since the technology first began to be used elsewhere."