NICOLA Sturgeon has described leaked UK Government revelations outlining substantial damage Brexit presents to the economy as a "watershed moment".

The First Minister accused Theresa May of a "cover up" after refusing to make public the analysis and said the case for a hard Brexit was "dead in the water".

Calling for the studies to be published in full, she said: "This devastating leak is a watershed moment in the Brexit negotiations. For months, Theresa May’s government have refused to produce any detailed analysis of the potential impact of various Brexit scenarios – now we know why they have so desperately engaged in a cover-up."

She pointed out that the UK Government’s analysis made clear that "leaving the EU will, in all circumstances, harm the economy of every nation and region in the UK" and that the findings underlined the case that remaining in the single market and customs union would "minimise the economic harm".

The leak of the UK Government's analysis comes just over two weeks after the First Minister published her own set of figures, which showed that the Scottish economy would contract by 8.5 per cent under a no deal scenario, costing each Scot £2,300 a year by 2030, a loss to the country of £12.7 billion a year.

"When the Scottish Government published our own impartial analysis a few weeks ago, showing an extreme Brexit could cost each person in Scotland £2,300 a year, the Tories accused us of scaremongering - now we find out that behind the scenes they agreed with us," Sturgeon said.

"The Prime Minister must now agree to publish this analysis in full, and any other analyses which they are concealing from the people of these islands.

"The case for a hard Brexit is dead in the water - and it is no wonder that, with every passing day, the extremists in the Tory party are becoming ever more desperate."

She added: "Time is running out and the chaos in Downing Street must end. Theresa May must face down the hard Brexiteers around her – and put jobs and living standards front and centre of the Brexit negotiations by remaining in the single market and customs union.”

The closely guarded UK Brexit impact analysis leaked to Buzzfeed News estimates that even if the Government opted to stay in the single market and customs union, there would be a 2 per cent hit to growth over a 15-year period.

With a comprehensive free trade agreement, the impact is forecast as a 5 per cent drop in growth, while a 'no deal' outcome would see a whopping 8 per cent knocked off growth over the same period of time.

All the figures were similar to those set out in the Scottish Government's report.

The UK paper, which has been drawn up by the Department for Exiting the EU, claimed that every sector of the British economy will suffer due to Brexit - the only exception being farming if the Government opts to adopt World Trade Organisation rules.

It also warned of an impact on the City of London, even if a free trade deal is agreed, and that all regions of the UK are likely to take a hit. The worst affected areas, the analysis claims, would be the north-east, the West Midlands and Northern Ireland.

The leaking of the document is a blow to Whitehall officials, who had reportedly tried to keep it under wraps ahead of one-to-one presentations to senior ministers this week.

A UK Government source played down the findings, saying the paper was an "early draft" and did not take account of the bespoke deal that Theresa May is aiming for with Brussels.

However a separate source in the Brexit department told Buzzfeed the report was not being made public "because it's embarrassing".

Labour MP Chris Leslie, a supporter of the pro-EU group Open Britain, said the paper showed the Government should change tack.

“It’s little wonder the Government has repeatedly refused to publish any serious Brexit analysis," he said.

"Their own impact assessments underline what has long been obvious, that their reckless plan to crash out of the Single Market and the Customs Union will leave us all much worse off."