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The cost of cutting migration from the EU after Brexit would be significantly greater than the benefits of a US trade deal, a leaked government analysis reportedly warns.

And new barriers to trade, such as loss of market access and customs and border checks would drive the cost of Brexit to the economy up even further.

According to the analysis, published tonight by BuzzFeed News , the scale of UK borrowing could be tens of billions of pounds higher in 15 years than if we had stayed in the EU.

The figures come from the same paper leaked to the site on Monday, which suggested Britain would be worse off under every single Brexit scenario projected by the government.

Elsewhere, the calculates a free trade deal with the United States could add 0.2% to UK growth - but even less stringent immigration policies than those favoured by the government would wipe out this benefit.

(Image: PA) (Image: Reuters)

Tory ministers caved in to pressure from Labour yesterday, agreeing to release the document to MPs.

But it will only provided on a single hard copy, to be held in a secure room in parliament for them to view - and will not be made available to the public.

The assessment, titled “EU Exit Analysis - Cross Whitehall Briefing” looked at the three most likely outcomes of Brexit.

If Britain is able to negotiate a comprehensive free trade deal with the EU, growth in the UK economy would be 5% lower over the next 15 years compared to current forecasts.

A “No deal” Brexit, in which the UK would revert to World Trade Organisation Rules, would see growth reduced by 8%.

(Image: PA)

And even in the softest Brexit option, under which we would retain single-market access, would see growth 2% lower than current forecasts.

In every scenario, almost every sector of the economy would see a negative impact from Brexit, as would every region in the country.

Labour MP and Best for Britain champion Tulip Siddiq said: ""This latest leak shows what a catastrophe the government's Brexit plans are in. It’s not ‘Taking back Control' - it’s making the country poorer.

"Theresa May’s catastrophic Brexit threatens everything from the NHS to the construction industry.

"The government are ignoring all the advice they are getting unless it agrees with the Hard Brexiteers on their backbenches. They are pandering to a few MPs in a desperate bid to avoid more letters landing in the safe of Graham Brady calling for a leadership election.

"Theresa May and her deluded immigration plan has been blown apart once and for all.

"The government have lied to the public for months about trade deals and Brexit reports. Tonight they have been caught red handed. It is time to make all of this analysis public and stop putting dogma above our economy."

A government spokesperson told BuzzFeed on Monday: “We have already set out that the government is undertaking a wide range of ongoing analysis in support of our EU exit negotiations and preparations.

"We have been clear that we are not prepared to provide a running commentary on any aspect of this ongoing internal work and that ministers have a duty not to publish anything that could risk exposing our negotiation position.”

A government source added: “As part of its preparations for leaving the European Union, officials from across Whitehall are undertaking a wide range of ongoing analysis.

"An early draft of this next stage of analysis has looked at different off-the-shelf arrangements that currently exist as well as other external estimates. It does not, however, set out or measure the details of our desired outcome – a new deep and special partnership with the EU – or predict the conclusions of the negotiations.

"It also contains a significant number of caveats and is hugely dependent on a wide range of assumptions which demonstrate that significantly more work needs to be carried out to make use of this analysis and draw out conclusions.”