SCOTLAND's largest petrochemical plant could close in 15 years unless an indigenous shale gas industry can be developed, according its owner.

Chemicals giant Ineos says the recently approved practice to import cheap shale gas from the USA for use in its chemical plants will not be cost-effective in the long term.

The company, which runs the huge refinery and petrochemicals plant at Grangemouth, on the Firth of Forth, recently acquired 729 sq miles of fracking exploration licences in central Scotland.

But the firm says the Scottish Government's moratorium on granting fracking licences could prevent the shale gas industry from developing in Scotland.

The development comes days after Scottish Labour leader Jim Murphy said he would use new powers in Holyrood to ban fracking, led to allegations of political posturing.

The Grangemouth facility is Scotland's biggest industrial site, employing about 1,000 staff and hundreds more on contract.

Ineos threatened to close the plant during a bitter industrial dispute in 2013 before unions accepted changes to pay and conditions.

The Scottish Government did not respond to the Ineos claim, except to say that the question of licensing powers for onshore oil and gas is subject of a consultation.

The Ineos move for licences would make it one of the biggest shale gas players in the UK.

It has already invested in an ethane supply project at Grangemouth which will allow the firm to import, store and use cheap shale gas from the US.

That formed part of its survival plan announced by Ineos in September, 2013.

Ineos Upstream chief executive Gary Haywood said it was not a long-term solution and was only expected to cover Grangemouth's needs for the next "10 to 15 years".

Speaking at a conference in Edinburgh he said it was feasible to get a shale industry up and running in the UK "within three to five years".

He added: "If you look forward five years, it is possible we could be producing gas from that point onwards.

"That would mean that we have some time to develop the resource and replace what we get from the US. Can we do that efficiently enough to make Grangemouth make sense in the future? That is a real challenge."

Commenting on the future of the plant without an indigenous shale gas supply, he said: "I think it is going to be very difficult because when you are shipping in material of that nature you are always at a disadvantage.

"It is a very special situation at the moment... with ethane being available in the US at very low prices, because of the rapid increase in production and the lack of demand in the US.

"That has meant we have been able to get that ethane at very, very cheap prices, relatively speaking.

"We can't see that going on. Unless we can develop an indigenous source, it is unlikely that the cracker (at Grangemouth) has a long-term future."

Scottish Conservative energy spokesman Murdo Fraser said: "This warning shows just how crucial it is for Scotland not to be left behind on fracking. It has revolutionised the US energy economy.

"It makes absolutely no sense for Grangemouth to be refining shale from across the Atlantic, while the SNP and Labour here either want to ignore fracking or ban it altogether.

"This vital plant has already been to the brink in recent years - we should take action now to ensure it doesn't return there any time soon."

Scottish Conservative energy spokesman Murdo Fraser said: "This warning shows just how crucial it is for Scotland not to be left behind on fracking.

"It makes absolutely no sense for Grangemouth to be refining shale from across the Atlantic, while the SNP and Labour here either want to ignore fracking or ban it altogether.

"This vital plant has already been to the brink in recent years - we should take action now to ensure it doesn't return there any time soon."

A Scottish Government spokesperson said: "The consultation will allow everyone with a view on this issue to feed it into government.

"Industry bodies including Ineos and the UK Onshore Operators Group welcomed the opportunity to engage in the consultation and environmental organisations including Friends of the Earth Scotland and WWF Scotland also both welcomed the announcement."