A hard Brexit would boost the incomes of Britain’s 19 million households by £5,000 a year, according to a group of pro-exit economists, who have urged the UK Government to abolish all trade barriers after leaving the European Union.

A report by the 16-strong Economists for Free Trade, led by Patrick Minford, the Cardiff University economics professor, claimed abolishing barriers such as tariffs could boost the economy by £135 billion a year, which would give households the £5,000 a year windfall.

But the plan was dismissed by Open Britain, which campaigns for closer ties with the EU, as "absurd" and a blueprint for "economic suicide".

Professor Minford, the report’s author, said: "Hard Brexit is good for the UK economically while soft Brexit leaves us as badly off as before. 'Hard' is economically much superior to 'soft'.

"Backers of Soft Brexit say it would preserve jobs but what they really mean is that it would preserve existing jobs by stopping competition from home and abroad.

"As every schoolboy knows and every politician ought to know, this aborting of competition reduces jobs in the long run.”

He added: "Competition increases productivity and so employment because higher wages paid for by higher productivity makes work more attractive. Competition also increases our general welfare because we are producing more."

Commenting on behalf of the Open Britain campaign group for close ties with the EU, Labour MP Alison McGovern said: "All anyone needs to know about this absurd plan is that its own author admits it would 'mostly eliminate manufacturing' in the UK.

"Unilaterally scrapping our tariffs without achieving similar reductions in the tariff rates of other countries would see Britain swamped with imports, leaving our manufacturers and farmers unable to compete.

"The levels of bankruptcy and unemployment, especially in industry and agriculture, would sky-rocket.”

She added: "This is a project of economic suicide, not prosperity. No responsible government would touch this report with a barge pole as a source of ideas for our future trade policy."

Prof Minford put forward his ideas in the run-up to June 2016's EU referendum, although he admitted in a column for the Sun: "Over time, if we left the EU, it seems likely that we would mostly eliminate manufacturing, leaving mainly industries such as design, marketing and hi-tech. But this shouldn't scare us."

Meanwhile, David Davis has warned the EU Union that "with the clock ticking" there is no point in negotiating aspects of Brexit twice in an attempt to push withdrawal talks towards discussions on a future trading relationship.

This coming week, the Brexit Secretary will publish five position papers further setting out Britain's negotiating strategy to add pace to the talks.

A key document is expected on the Government's favoured approaches to enforcing rights outside the jurisdiction of the European Court of Justice.

Disagreement over the ECJ's role was a major sticking point during July's round of talks with the UK aghast at Brussels' insistence that EU citizens' rights should be enforced by the court after Brexit.

This week's paper will set out different possible approaches to end the "direct jurisdiction" of the ECJ but still enforce individuals' and businesses' rights after Brexit.

But first, a document on goods will emphasise the Government is seeking a deal to ensure the freest and most friction-less trade possible in goods and services.

At present, the EU's position is that only goods should be discussed in "phase one" of the negotiations, in which "sufficient progress" must be made before talks on a future trade deal can begin.

However, the UK Government believes the goods and services sectors are impossible to separate and so wants to discuss them together.

Mr Davis said: "With the clock ticking, it wouldn't be in either of our interests to run aspects of the negotiations twice."

He went on: "This week we set out more detail of the future relationship we want with the European Union, putting forward imaginative and creative solutions to build a deep and special partnership with our closest neighbours and allies.

"In the coming days we will demonstrate our thinking even further, with five new papers; all part of our work to drive the talks forward and make sure we can show beyond doubt that we have made sufficient progress on withdrawal issues by October so that we can move on to discuss our future relationship."

Another position paper on confidentiality will make clear the Government's intentions on ensuring official documents and information exchanged between the UK, EU and other member states remain protected after Brexit.

A document will also be published on civil judicial co-operation to reassure the domestic legal sector and with an eye on August's talks.

And a paper on data will seek to ensure that it continues to be passed between the UK and EU without disruption.

Writing in the Sunday Times, Mr Davis said some early discussion of the future trading relationship would help progress on the Irish border, a key issue in phase one of withdrawal talks.

"It is simply not possible to reach a near final agreement on the border issue until we've begun to talk about how our broader future customs arrangement will work," he said.

"Furthermore, if we get the comprehensive free trade agreement we're seeking as part of our future partnership, solutions in Northern Ireland are easier to deliver."

Meanwhile, Sir Paul Jenkins, who was the Government's most senior legal official for eight years until 2014, said Britain would have to replicate EU rules and submit to the ECJ "in all but name" if it wanted to remove the need for hard borders.

Last week, the Government published a paper setting out its wish for close customs arrangements with the EU and no hard border between Northern Ireland and the Republic of Ireland.

"If the UK is to be part of something close enough to a customs union or the single market to remove the need for hard borders, it will only work if the rules are identical to the EU's own internal rules," Sir Paul told the Observer.

"Not only must they be the same but there must be consistent policing of those rules. If Theresa May's red line means we cannot be tied to the ECJ, the Brexit treaty will need to provide a parallel policing system.

"That may be a new court but, in reality, any new court will have to follow what the ECJ says about the EU's own rules, otherwise the new system won't work. So, never mind Theresa May's foolish red line; we will have the ECJ in all but name,” he added.