Studies expected to show the UK will gain little from post-Brexit trade deals with the US and the big Asian economies are being suppressed by the government, The Independent can reveal.

Analyses were completed as long ago as 2017 into the probable impact on growth from agreements long hailed as the prize for leaving the EU, but ministers are refusing to release them.

One trade expert said he had little doubt they were being concealed because they would – like independent studies – reveal that significant damage from new trade barriers with the continent will far outweigh the gain from other deals.

Alan Winters, professor of economics at the University of Sussex, joined with Labour in calling on ministers to reveal what they had been told, saying: “The entire Brexit debate has been conducted in a great fog of obfuscation.”

Paul Blomfield, Labour’s Brexit spokesperson, said: “These reports must be released immediately. If Boris Johnson wants to risk European trade to secure a deal with Donald Trump, we need to know the cost.”

Economists have estimated that will deliver a hit to the UK economy of anything between £70bn and £130bn in the long run, leaving people thousands of pounds worse off.

Now, in response to a freedom of information request submitted by The Independent, the Department for International Trade (DIT) has said internal analysis into other trade deals is “a work in progress”.

But it also revealed academics at the Centre for Economic Policy Research had evaluated the benefits from a US deal, an agreement with Japan and from membership of the CPTPP, a trade partnership of 11 Pacific nations.

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The last two were completed in August 2019 – while the study into an agreement with Washington has been gathering dust since July 2017.

Brexiteers have called for the UK to join Japan, Malaysia, Singapore, Australia, New Zealand, Mexico, Chile and others in the CPTPP, despite the UK being thousands of miles from the Pacific.

And Dominic Raab, the foreign secretary, recently spent several days in the region, saying: “Now is the time to put global Britain into action. The Asia-Pacific region is full of opportunities.”

However, DIT has refused to release any of the three studies, citing an exemption “if information clearly relates to the development of government policy”.

“Premature release of this analysis would be detrimental to the progress of future trade discussions once the UK has left the EU,” the department said.

Professor Winters, of the UK Trade Policy Observatory at the University of Sussex, said: “If the government thought it had a very strong case that these deals would be big and strong then they would publish these studies.

“It’s an indication that there’s nothing there. To the extent that we have any analysis, it suggests that the benefits of these deals are very small.

“And, with any modelling, what we gain from an agreement with the US and Japan is a lot smaller than what we lose from the EU.”

And Mr Blomfield added: “The government is embarking on the most important negotiations in our postwar history. The British people deserve to know the impact of the decisions being made on their behalf.”

However, a Downing Street spokesperson said: “New FTAs represent a significant economic opportunity. With new freedoms to strike these ourselves, independently, we can open up our markets, increase wages and improve living standards across the UK.”

In the last parliament, Labour was able to secure the release of similar studies by laying a “humble address”, but this route has been shut off by the 80-strong Conservative majority.

The secrecy leaves a November 2018 Treasury document as the only official forecast – putting the GDP gain from deals with the US, Australia and New Zealand at a puny 0.2 per cent.

It has frequently been dismissed by Brexit-backing Tories because Philip Hammond, the then-chancellor, opposed a hard Brexit – but has not been updated.

The hoped-for US deal is already in trouble over Washington demanding access for lower-quality agricultural goods and to the NHS drugs market, and because of the bust-up over the UK’s planned tech tax.