Sir Keir Starmer will later promise to “make Brexit work” as he outlines his party’s plan to “end the Brexit divisions once and for all”.
The Labour leader will rule out re-joining the EU if he wins the next election, as well pledging not to go back into the single market, customs union or returning to free movement agreements.
Instead, he will commit to “sort out the poor deal Boris Johnson signed” with a five-point plan, including tackling issues with the Northern Ireland Protocol, which has dominated discussions since the UK left the bloc.
Speaking at the the Centre for European Reform on Monday evening, Sir Keir will say: “There are some who say, ‘we don’t need to make Brexit work, we need to reverse it’, [but] I couldn’t disagree more.
“Because you cannot move forward or grow the country or deliver change or win back the trust of those who have lost faith in politics if you’re constantly focused on the arguments of the past.
“We cannot afford to look back over our shoulder. Because all the time we are doing that we are missing what is ahead of us.”
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Point one of Labour’s plan will be addressing the protocol, which Sir Keir will say “has to be the starting point” to make Brexit work.
The treaty was agreed by the UK and EU to avoid a hard border being introduced on the island of Ireland after Brexit.
But it led to a trade barrier in the Irish Sea, causing problems on moving goods between Great Britain and Northern Ireland, and angering unionists – including the DUP, who have refused to form a government in Stormont until the protocol is scrapped.
Sir Keir will say businesses in Northern Ireland and Ireland have told him they can make the protocol work, but the Conservative government had “eroded trust” between the two sides.
“Labour will change that,” he will say. “We will be the honest broker our countries need. We will get the protocol working and we will make it the springboard to securing a better deal for the British people.”
He will also pledge to “eliminate most border checks created by the Tory Brexit deal” with a new veterinary agreement for agricultural products, and put in place “a better scheme to allow low-risk goods to enter Northern Ireland without unnecessary checks”.
The proposals come as the UK government is pushing forward with the controversial Northern Ireland Protocol Bill, allowing it to ditch parts of the deal signed by Mr Johnson in 2019.
Northern Ireland Secretary Brandon Lewis previously told Sky News that action was needed to fix the “substantial problems” caused by the implementation of the agreement.
But critics, including former Prime Minister Theresa May, have warned the legislation would break international law and damage the UK’s standing.