Theresa May has signed the letter that will formally begin the UK’s departure from the European Union.
Giving official notice under Article 50 of the Lisbon Treaty, it will be delivered to European Council president Donald Tusk later.
In a statement in the Commons, the prime minister will then tell MPs this marks “the moment for the country to come together”.
It follows June’s referendum which resulted in a vote to leave the EU.
Mrs May’s letter will be delivered at 12:20 BST on Wednesday by the British ambassador to the EU, Sir Tim Barrow.The prime minister, who chaired an hour long cabinet meeting earlier, has left Downing Street to make a statement to MPs confirming the countdown to the UK’s departure from the EU is under way.She will promise to “represent every person in the whole United Kingdom” during the negotiations – including EU nationals, whose status after Brexit has yet to be settled.
“It is my fierce determination to get the right deal for every single person in this country,” she will say.
“For, as we face the opportunities ahead of us on this momentous journey, our shared values, interests and ambitions can – and must – bring us together.”Attempting to move on from the divisions of June’s referendum, Mrs May will add: “We are one great union of people and nations with a proud history and a bright future.
“And, now that the decision has been made to leave the EU, it is time to come together.”
Labour leader Jeremy Corbyn said his party respected the decision to leave the EU and would hold the government to account “every step of the way”.
He said: “Britain is going to change as a result. The question is how.”
Mr Corbyn warned it would be “a national failure of historic proportions” if Mrs May does not secure protection for workers’ rights.
Chancellor Philip Hammond said the triggering of Article 50 was “a pivotal moment for Britain” and insisted the government “will get a deal”.
But he suggested on BBC Radio 4’s Today programme that ministers would be prepared to compromise during the process, adding: “Everybody in the EU and the UK is going to go into this negotiation looking to protect their own interests…
“We understand that we can’t cherry-pick, we can’t have our cake and eat it – that by deciding to leave the EU and negotiate a future relationship with the EU as an independent nation, there will be certain consequences of that and we accept those.”
He said EU citizens could still move to the UK and have their full rights while the UK remains “full members of the EU for the next two years”.
But crossbench peer Lord Gus O’Donnell, formerly Britain’s top civil servant, likened the triggering of Article 50 to being “in a plane being flown by members of the EU and we’re about to jump out and we have got a parachute designed by the people flying the plane – and they have designed it in a way to deter anyone else jumping out”.