Campaigners against a potential 'super-quarry' near St Keverne are celebrating after the government overturned permission for preliminary works on environmental grounds.

Shire Oak Energy, the company that wants to take stone from Dean Quarry to build a new tidal energy lagoon in Swansea, hit a stumbling block after Greg Clark, Secretary of State for Communities and Local Government, overturned planning permission which had been granted by Cornwall Council in April.

In a letter to the council, Mr Clark said that an Environmental Impact Assessment (EIA) should have been carried out prior to permission being granted for the work, which includes a perimeter fence, fuel and explosive storage, and office, reception and amenity areas at the site.

He wrote that the "nature, size or location" of the quarry would be likely to have "significant effect" on the environment, and noted concerns raised by Natural England over the Coverack to Porthoustock Site of Special Scientific Interest (SSSI), The Lizard Special Area of Conservation and the recently appointed Manacles Marine Conservation Zone (MCZ).

The letter was received on the same day as Amber Rudd, Secretary of State for Energy and Climate Change, gave the green light to the construction of world’s first tidal lagoon power station in Swansea Bay, and Dean Quarry is one of the frontrunners to supply armour stone to build the project. The success of the lagoon could lead to several more being built around the Welsh coast, with resulting demand for more rock.

Campaign Against Dean Superquarry (CADS), a group which has been vocal in its campaign against reopening the quarry, have hailed the decision by the secretary of state.

The group had felt the works approved by Cornwall Council were what local Cornwall COuncillor Walter Sanger called 'salami slicing' development, getting the less contentious applications through planning ahead of larger plans which would include a jetty and 535 metre breakwater built on top of the MCZ.

Alison McGregor, from CADS, said the breakwater would be a test case for MCZs and if the government allowed it "there would be no point in having an MCZ, everybody might just as well pack up and go home."

She said the announcement was "a positive step, a step in the right direction."

She said: "We felt that the size and scale of the development meant that they should have done an EIA, and the council waved it through without the need for one."

But she added: "We must think of it like the Grand National, and we've got over the first fence, but there are more fences ahead."

A spokesperson for Shire Oak Energy said the company is awaiting guidance from Cornwall Council before taking any decisions or making a statement.

Cornwall Council said in a statement: "At the time the application was being considered, the council issued its own EIA screening opinion in the normal way and concluded the development under consideration did not require an EIA.

"The council is currently considering the findings and implications of the Secretary of State’s decision."

It declined to answer questions on why an EIA was not deemed necessary, or whether it will appeal the decision.