Continued uncertainty over Britain’s future trading relationship with the EU could cost the UK economy £4.4bn annually by the end of this year and £15bn by the end of the decade, a new report has warned.

Despite Boris Johnson’s claim to be “getting Brexit done” the report by international think tank Rand Europe found that the UK’s formal departure from the EU on Friday will “only end the first phase of trade uncertainty” caused by Brexit.

And the paper gave short dismissal to the prime minister’s promise to conclude negotiations on a Canada-style free trade agreement by the end of a so-called “transition period” on 31 December, warning that talks “may take considerable time” as the UK comes to terms with the “negative long-term economic implications” of a swift deal.

Damage to the UK economy will carry on accelerating until details of the new arrangements are finally settled, with GDP growth potentially reduced by £11bn by 2025 and £15bn by 2029 unless a new deal is reached.

The report warned that any decline in GDP will feed through into higher government borrowing, at an additional cost in annual interest payments of almost £1.3bn by the end of 2020 and £3bn by 2025.

Best pictures from Final Say Brexit march Show all 76 1 /76 Best pictures from Final Say Brexit march Best pictures from Final Say Brexit march Crowds march through central London Getty Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march Protesters gather in Parliament Square Led By Donkeys Best pictures from Final Say Brexit march Mayor of London Sadiq Khan joins protesters PA Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march Anti-Brexit protesters fill Parliament Square in London PA Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march A demonstrator marches EPA Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march People's Vote Final say march - 19 October 2019 Angela Christofilou Angela Christofilou/The Independent Best pictures from Final Say Brexit march Protesters push a float depicting Dominic Cummings using Boris Johnson as a puppet during the Final Say Brexit march in London PA Best pictures from Final Say Brexit march EU supporters react after the result of the vote on the deal delay was announced at the House of Commons REUTERS Best pictures from Final Say Brexit march A demonstrator carries his dog draped in EU flag AP Best pictures from Final Say Brexit march Thousands of people taking part in a People's Vote march AFP/Getty Best pictures from Final Say Brexit march Protesters use their flags to shelter from the rain Getty Images Best pictures from Final Say Brexit march Protesters march towards Parliament Square Getty Images Best pictures from Final Say Brexit march Anti-Brexit demonstrators carry placards and EU flags AP Best pictures from Final Say Brexit march Sir Oliver Letwin MP in Parliament Square, London, during an an anti-Brexit, Let Us Be Heard rally, after it was announced that the Letwin amendment, which seeks to avoid a no-deal Brexit on October 31, has been accepted PA Best pictures from Final Say Brexit march Thousands of people taking part in a People's Vote march UK BROADCASTERS POOL/AFP via Get Best pictures from Final Say Brexit march A protester with "Bollocks to Brexit" stickers on his head Getty Images Best pictures from Final Say Brexit march Demonstrators march EPA Best pictures from Final Say Brexit march Britain's main opposition Labour Party shadow Secretary of State for Exiting the EU Keir Starmer, shadow Home Secretary Dianne Abbott, shadow Chancellor of the Exchequer John McDonnell, shadow Foreign Secretary Emily Thornberry speaks on stage in Parliament Square AFP via Getty Images Best pictures from Final Say Brexit march Anti-Brexit supporters cheer outside parliament AP Best pictures from Final Say Brexit march A EU supporter waves flags REUTERS Best pictures from Final Say Brexit march Anti-Brexit supporters AP Best pictures from Final Say Brexit march Protesters shout and chant demanding a final say Getty Images Best pictures from Final Say Brexit march Police look towards protesters Getty Images Best pictures from Final Say Brexit march Pro-Brexit protesters outside the Houses of Parliament in London PA Best pictures from Final Say Brexit march People taking part in an Anti-Brexit, Let Us Be Heard march head to Parliament Square in London PA Best pictures from Final Say Brexit march People taking part in an Anti-Brexit, Let Us Be Heard march in Trafalgar Square PA Best pictures from Final Say Brexit march Anti-Brexit supporters cheer outside parliament AP Best pictures from Final Say Brexit march People taking part in an Anti-Brexit, Let Us Be Heard march past Trafalgar Square PA Best pictures from Final Say Brexit march Protesters shout and chant Getty Images Best pictures from Final Say Brexit march Cory (7) sits on his father's shoulders as protesters march towards Parliament Square Getty Best pictures from Final Say Brexit march People attend the 'Together for the Final Say' march EPA Best pictures from Final Say Brexit march Protesters march towards Parliament Square Getty Images Best pictures from Final Say Brexit march Mayor of London Sadiq Khan speaks on stage PA Best pictures from Final Say Brexit march A woman in EU costume EPA Best pictures from Final Say Brexit march Anti-Brexit protesters fill Parliament Square in London PA Best pictures from Final Say Brexit march Anti-Brexit protesters AP Best pictures from Final Say Brexit march Anti-Brexit protesters hold an Independent banner Angela Christofilou/The Independent Best pictures from Final Say Brexit march Protesters hold an anti-Brexit placard by The Independent stall during the Final Say Brexit march in London Tom Richell Best pictures from Final Say Brexit march Anti-Brexit protesters in Parliament Square, London, PA Best pictures from Final Say Brexit march Demonstrators hold placards and EU flags AFP/Getty Best pictures from Final Say Brexit march An anti-Brexit protester joins in the Final Say Brexit march on 19 October AP Best pictures from Final Say Brexit march EU supporters march in London REUTERS Best pictures from Final Say Brexit march Sir Patrick Stewart and Paul McGann join in the Final Say Brexit march in London on 19 October PA Best pictures from Final Say Brexit march EU supporters march Reuters Best pictures from Final Say Brexit march A demonstrator shouts into a megaphone as she marches AFP via Getty Images Best pictures from Final Say Brexit march A dog dressed in an anti-Brexit placard is walked in the Final Say Brexit march in London EPA Best pictures from Final Say Brexit march EU supporters march REUTERS Best pictures from Final Say Brexit march A morris dancer takes part in the Final Say Brexit march in London PA Best pictures from Final Say Brexit march Whippets are dressed in EU flag clothing during the Final Say Brexit march in London AP Best pictures from Final Say Brexit march Protesters march towards parliament in the Final Say Brexit march in London on 19 October 2019 PA Best pictures from Final Say Brexit march An anti-Brexit demonstrator takes part in the Final Say Brexit march in London AFP/Getty Best pictures from Final Say Brexit march EU supporters call on the government to give Britons a vote on the final Brexit deal Reuters Best pictures from Final Say Brexit march Anti-Brexit protesters Angela Christofilou/The Independent Best pictures from Final Say Brexit march An anti-Brexit protester Angela Christofilou/The Independent Best pictures from Final Say Brexit march Anti-Brexit protesters demonstrate in London during the Final Say Brexit march on 19 October AP Best pictures from Final Say Brexit march Protesters push a float depicting Dominic Cummings using Boris Johnson as a puppet during the Final Say Brexit march in London AFP/Getty Best pictures from Final Say Brexit march Protesters march towards parliament from Park Lane in the Final Say Brexit march in London on 19 October 2019 PA Best pictures from Final Say Brexit march Marchers visit The Independent stall during the Final Say March in London Tom Richell Best pictures from Final Say Brexit march An anti-Brexit protester holds a sign calling for a Final Say during a march in London EPA

Mr Johnson’s insistence that he will not extend the transition beyond the end of 2020 has created the risk of a no-deal Brexit on disadvantageous World Trade Organisation (WTO) terms, sparking business anxiety about tariffs and quotas on exports.

The report warned that the PM will have a difficult judgment to make on the balance of costs to the UK between cutting talks short or allowing them to continue too long.

“The UK will need to weigh up the potential short-term economic implications of prolonged trade policy uncertainty if negotiations last beyond 31 December 2020, versus the potential negative long-term economic implications of an agreement that is made quickly but lacks the comprehensiveness required for a broad and deep future UK-EU trading relationship,” it said.

“Britain’s allies, especially the US, will also be concerned by any prolonged period of uncertainty about the UK’s security and defence relationships with its neighbours.

“In all these senses, 31 January 2020 is just the end of the beginning.”

The report found that Britain has already suffered “negative economic consequences” due to the 2016 referendum decision to quit the EU, as consumers reined in spending and businesses held back from investment even though the terms under which the UK trades did not change.

Boris Johnson signing the withdrawal agreement which will take the UK out of the EU (Crown Copyright)

The report’s author, Rand vice president Charles Ries, said: “We found that the negative economic effects on both GDP and government borrowing are tangible and increase over time.

“Uncertainty around the future trading relations with the EU and the expected future increase in trade barriers, either through tariffs or non-tariffs, potentially affects firms’ foreign trade and investment decisions.”