NICOLA Sturgeon has refused to endorse a £1.5 billion investment that will see weekly deliveries of American fracking gas arrive in Scotland, despite the new supply line protecting the livelihoods of 10,000 workers.

Chemicals giant Ineos this week welcomed the first shipment of US shale gas to Scotland and said its outlay on new infrastructure and eight huge purpose built ships to transport ethane from the US had prevented the closure of the crucial Grangemouth petrochemical plant and refinery.

Asked at Holyrood by Ruth Davidson whether she was in favour of shale gas being used in Scotland, the First Minister highlighted the SNP's moratorium but did not address the issue of the imports. The Scottish Tory leader then accused Ms Sturgeon of displaying "total double standards" over the issue by talking up her environmental credentials while ignoring fracked gas being "poured into a tanker and shipped all the way across the Atlantic".

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The First Minister said it was Ineos that moved to bring in shale gas, and is "absolutely free to take such decisions." She added: "Ineos, of course, is an extremely important company in the Scottish economy."

However, she did not say whether she approved of the imports, which were slammed as "completely unacceptable" by Friends of the Earth Scotland as they would prop up Grangemouth "on the back of environmental destruction across the Atlantic".

Her spokesman later declined repeated invitations to clarify her stance, repeating remarks Ms Sturgeon had made in the chamber about the importance of Ineos but refusing to say whether she backed its investment and the shipping of shale gas to Scotland.

The position clashes with those of SNP representatives for the Grangemouth area in both Holyrood and Westminster, who despite being against fracking, a process that sees water, sand and chemicals pumped deep underground to fracture shale rock, both welcomed the firm's investment. Angus MacDonald, the MSP for Falkirk East, hailed the arrival of the shale gas as positive for the local economy and Scotland as a whole.

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Ms Sturgeon was challenged over fracking after SNP ministers snubbed invitations to attend the Ineos celebration of the first shale gas import, in a move that was described as "disappointing" by billionaire company boss Jim Ratcliffe and "absolutely shocking" by another senior source at the firm.

Murdo Fraser, the Tory economy spokesman, said: "The SNP’s approach to this arrival was infantile and insulting, and it’s astonishing that the First Minister continues to refuse to welcome the development."

It has also emerged that key scientific reports commissioned by the Scottish Government, which will inform a decision over whether to lift the moratorium or turn it into a full fracking ban, have been delayed. Initially promised by the summer, Ms Sturgeon said they will now come out within "a few weeks".

Her spokesman refused to commit to publication ahead of the SNP conference, beginning on October 13, with a vocal group of grassroots members keen for the party leadership to take a tougher stance on unconventional oil and gas and fracking proving a controversial topic at previous gatherings.

Ms Sturgeon insisted her Government would take a "cautious, evidence-based approach to shale gas and fracking" as opposed to the Tories, the only Holyrood party to support the process.

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She said: "I appreciate that the Scottish Conservatives’ position on fracking in Scotland is to ride roughshod over local opinion and the range of environmental and other concerns that have been raised."

Meanwhile, Ms Davidson was accused of hypocrisy by the SNP after posing for Stop Climate Chaos photocall at Holyrood 30 minutes after she had backed fracking in the Holyrood chamber.

Party MSP Graeme Dey, a member of Holyrood's environment committee, said: "One minute Ruth Davidson is demanding a gung-ho approach to fracking underneath people’s homes in Scotland. The next, she’s posing as some sort of climate champion."