NICOLA Sturgeon has described the leaking of UK Government’s secret Brexit impact report as a “watershed moment”.

The First Minister accused Theresa May of a “cover-up” for not making public the analysis of how badly Britain would be hurt by leaving the EU.

Journalists were never supposed to see the report, which pulled together the Government’s official economic analyses of different Brexit scenarios.

READ MORE: EU leaders say no surprises in leaked Brexit report

A hard copy has been making its way round key Cabinet ministers this week. So scared was the government of the papers being leaked to the press that the physical copy was taken away after they had seen it.

According to the forecasts by the civil servants, there is no scenario or possible outcome of Brexit that will not result in damage to the economy.

Officials believe that even if London can negotiate a comprehensive free trade agreement with the EU, growth would be five per cent lower over the next 15 years than if we were to stay within the European Union.

If the UK crashes out of the EU without a deal, a so-called hard Brexit, and relies on the World Trade Organisation, then growth reduces by eight per cent. Even a soft Brexit, where the UK would remain in the single market through membership of the European Economic Area would lower growth by two per cent.

That, however, is unlikely to happen, with both the Tories and Labour ruling out any deal that would mean having to accept freedom of movement.

In many ways, there is little new in the document. It reflects other research carried out, including analysis published by the Scottish Government just two weeks ago.

However, it is confirmation that the UK Government knows that Brexit will damage the economy, and that they have kept that information from the public.

“This devastating leak is a watershed moment in the Brexit negotiations,” Sturgeon said.

“For months, Theresa May’s Government has 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.

“The UK Government’s own analysis makes clear that leaving the EU will, in all circumstances, harm the economy of every nation and region in the UK – and underlines the case that remaining in the single market and customs union is the best way to minimise that economic harm. Sturgeon added: “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.”

In the Commons, the Government tried to play down the significance of the leak, and, in incredible scenes, attacked the civil servants who had compiled the research.

Brexit Secretary David Davis ducked the questions, with his junior, Steve Baker, taking his place.

In one question about economic forecasting, Baker even seemed to channel Michael Gove, who, during the EU referendum campaign, said “people in this country have had enough of experts”

Throwing his civil servants under the bus, Baker told Parliament: “I am not able to name an accurate forecast, and I think that they are always wrong.”

Despite that, he also stressed, the leaked study showed economic growth was still predicted “in all scenarios” of Brexit.

Baker said work on the report wasn’t yet complete, and for some reason didn’t include any assessment of what the Government actually wants out of its negotiations with Europe.

The Tory said the leak and the article on Buzzfeed revealing its contents were “a selective interpretation of a preliminary analysis”.

“It is an attempt to undermine our exit from the European Union,” Baker added.

He went on: “Even the ministerial team in my department has only just been consulted on this paper in recent days and we’ve made it clear it requires significant further work.

“In fact, I only saw this report myself this morning.”

Labour’s shadow Brexit secretary, Keir Starmer, told him: “Not good enough.”

“We have been here before. It took a great deal of time last year and the use of a humble address to force the Government to release documents relating to Brexit.”

Baker was sarcastically clapped and heckled when he said the “economic analysis is not what’s known formally as an impact assessment”.

The SNP’s Joanna Cherry got no answer when she asked Baker why, if the impact reports were incorrect, the Government doesn’t “tell the British people what it wants from the EU by way of a deal and cost it out and publish the results?”

He insisted the Prime Minister had, so far, been very clear.