Scotland has placed a moratorium on underground coal gasification, a form of unconventional gas extraction, adding to a ban on shale gas that it imposed in January in conflict with the pro-shale stance of Prime Minister David Cameron.

The Scottish government also said on Thursday it would start an in-depth investigation into the impact of shale gas fracking, the process whereby water, sand and chemicals are blasted at underground rocks to release trapped gas.

The outcome of the consultation in spring 2017 will then allow Scottish ministers to decide whether to keep the shale gas moratorium in place or not.

The development of shale gas projects has split opinions in Britain, with the central government seeing huge economic benefits from tapping domestic gas supplies, while many others are concerned about the technique's impact on the environment, local house prices and tourism.

Cameron has promised to go "all out" for shale gas, hoping to replicate some of the success in bringing down domestic energy prices and reducing import dependence which the U.S. has seen from a huge boom in shale gas and oil exploration.

Scottish Energy Minister Fergus Ewing said the in-depth consultation showed Scotland was more cautious about shale gas development, as opposed to "the gung-ho approach of the UK government".

Underground coal gasification (UCG), a form of gas extraction where oxidants are injected into underground coal deposits to heat them to temperatures that allow gas to escape, will undergo a separate assessment, led by Campbell Gemmel, a professor of environment research at the University of Glasgow, the Scottish government said.

Scotland's leading Scottish National Party, which will hold its annual party conference next week, welcomed the UCG moratorium on Thursday.