Boris Johnson is to attempt to reassure voters who are angry and alienated by Brexit that the UK’s split from the EU is a cause for “hope not fear”.
The foreign secretary will use a speech to try to build bridges with those who voted to remain in the EU, saying their belief in European solidarity is based on “noble sentiments”.
“It is not good enough to say ‘you lost, get over it’,” he will say.
But he will also insist those who want to stop Brexit cannot prevail.
In the speech in London, he will say that that holding another referendum on the UK’s membership of the EU would be a “disastrous mistake that would lead to permanent and ineradicable feelings of betrayal”.
Labour MP Chuka Umunna, who supports the Open Britain campaign “against a hard, destructive Brexit”, said Mr Johnson was “totally unqualified to preach about the perils of fear and betrayal”, having “engaged in disgraceful scaremongering” during the EU referendum.
Mr Johnson’s speech is the first in a series of speeches by Theresa May and her ministers on the “road to Brexit”.
The prime minister is expected to address the UK’s future relations with the EU in a speech in Munich on Saturday, the day after she holds talks with German Chancellor Angela Merkel in Berlin.
In what has been billed as his most substantial speech on Brexit for more than a year, Mr Johnson – a leading figure in the Leave campaign during the 2016 referendum – is expected to make the “liberal case” for the UK’s withdrawal and argue it will allow the country to play a greater role on the world stage.
Excerpts released in advance of the speech suggest Mr Johnson will appeal to both sides to move on from the divisions of the past and unite around a shared goal of seeing an outward-facing and global nation succeed.
“We must accept that many [Remainers] are actuated by entirely noble sentiments, a real sense of solidarity with our European neighbours and a desire for the UK to succeed,” he will say.
“If we are to carry this project through to national success – as we must – then we must also reach out to those who still have anxieties.
“I want to try to anatomise at least some of those fears and to show to the best of my ability that they are unfounded and that the very opposite is usually true: that Brexit is not grounds for fear but hope.”
by Ben Wright, political correspondent, BBC News
It’s a conciliatory tone we haven’t heard much from Cabinet ministers.
And it’s a recognition of the deep divisions Brexit has opened. Boris Johnson will use his Valentine’s Day speech to try to woo despairing Remain supporters who think Brexit is a disaster.
There’s no crumb of comfort for people who would like to see Brexit stopped. Mr Johnson insists it must happen.
Furthermore, he will say the UK must take back full control of regulations and tariff schedules.
It’s no secret the Cabinet is divided on how closely the UK and EU should align after Brexit.
Last month the Chancellor Philip Hammond said he wanted the two economies to move apart only “very modestly”, a statement that enraged Brexiteers.
Boris Johnson’s speech shows again that he is not in the close alignment camp.
His speech was approved by Number 10 and will be scoured for clues about how Theresa May’s divided Cabinet plans to find common ground around the deal it hopes to strike with the EU.
Continuing the conciliatory tone in an article for the Sun, Mr Johnson writes: “To those who worry that we are somehow going to become more insular, the exact reverse is true.
“We do not want to haul up the drawbridge and we certainly don’t want to deter the international students who make a huge contribution to our economy.”
Mr Johnson is expected to focus on the potential for extending British influence in the rest of the world, exploiting Britain’s traditional strengths in trade, diplomacy, soft power, development and human rights.
The foreign secretary, who returned on Tuesday from a visit to Myanmar and Thailand, told the Guardian last month he would like to see the UK “taking advantage” of the people’s decision to leave to get the “best economic result from that decision, and do the best we can do”.
Ministers are under pressure to spell out how they can square their desire for frictionless trade after Brexit with the UK’s exit from the single market and customs union, which EU officials say will create trade barriers.
By leaving the customs union, the UK has said it will have freedom to negotiate trade deals of its own during the transition period, while reducing tariffs on imports from developing countries.
Mr Johnson is one of the most enthusiastic Brexiteers in the cabinet but his decision to deliver a Brexit speech shortly before Mrs May’s Florence speech in October, plus his recent plea for more money to be spent on the NHS after Brexit, has seen him face criticism from some in his party.
Meanwhile, a report by the Commons Home Affairs Committee has said the UK is ill-equipped to cope with changes to the immigration system after Brexit due to a lack of resources.
A group of MPs has warned that the Home Office is planning only “moderate adjustments for an immense bureaucratic challenge”.
The Home Office said preparations for Brexit were well advanced and more staff were being recruited.