Theresa May has vowed to restore Britain's "self-determination" as the letter confirming our EU divorce was finally delivered - including a warning to Brussels that punishing the UK would be a "costly mistake".
The Prime Minister delivered an upbeat vision of a UK whose "best days lie ahead" as she confirmed her envoy Sir Tim Barrow had handed the formal notification to European Council president Donald Tusk in Brussels.
She also insisted she wanted to forge a "special partnership" with the Brussels club and appealed for 'constructive' engagement during the looming negotiations.
But the letter also included a stark threat about the "fragile" condition of the EU and warned that efforts to give Britain a bad deal would be seriously damaging for the bloc's own prosperity and security.
As the point of no return was reached, May told the House of Commons that she was "giving effect to the democratic will of the UK people".
"The Article 50 process is now underway...
In accordance with the wishes of the people, the United Kingdom is leaving the EU.
"This is a historic moment from which there can be no turning back."
She added: "At moments like this, a great turning point in our nation’s story, the choices we make will define the character of our nation.
"We can choose to say the task will be too great, we can choose to turn our face to the past and say it can’t be done.
"Or we can look forward and in believe in the enduring power of the British spirit.
"I choose to believe in Britain and that our best days are to come."
The six-page letter was handed over some eight months after the people delivered their verdict in the EU referendum.
It confirms that Britain will be leaving the single market, but wants a broad free trade agreement, and will seek an early deal to guarantee rights for EU nationals already here and Britons living on the continent.
But the missive also included a chilling warning to Brussels against trying to take revenge on the UK for leaving.
"At a time when the growth of global trade is slowing and there are signs that protectionist instincts are on the rise in many parts of the world, Europe has a responsibility to stand up for free trade in the interest of all our citizens," the letter said. "Likewise, Europe’s security is more fragile today than at any time since the end of the Cold War. Weakening our cooperation for the prosperity and protection of our citizens would be a costly mistake."
Tusk jibed about the length of time it had taken May to begin the process, and urged people not to "pretend this is a happy day in Brussels or London".
He insisted the EU will act "constructively" but "as one" and was determined to "preserve our interests".
May briefed the Cabinet on the task ahead this morning, after putting her signature to the letter last night before it was transported to Belgium on the Eurostar by diplomats and guards.
In a bid to spike the guns of nationalists in Scotland, May told the Commons this afternoon that Edinburgh, Cardiff and Belfast would be stronger after Brexit.
She told MPs: "No decisions currently taken by the devolved administrations will be removed from them.
"I expect the devolved administrations will see significant increases in their decision making powers as a result of this process."
In a plea for unity, May said the UK should be "no longer defined by the vote we cast, but by our determination to make a success of the result".
'We are one great union of people and nations with a proud history and a bright future,' she added.
"This great national moment needs a great national effort," she said.
May said Britain would continue to be willing allies and close friends with Europe. She said: "With European security more fragile today than at any time since the cold war, weakening our cooperation and not standing up for European values would be a costly mistake.
"Our decision to leave the European Union was no rejection of European values."
May’s letter to Tusk made clear she was implementing the "democratic decision" of the referendum and setting out Britain’s objectives.
"We believe that these objectives are in the interests not only of the United Kingdom but of the European Union and the wider world too," it said.
"It is in the best interests of both the United Kingdom and the European Union that we should use the forthcoming process to deliver these objectives in a fair and orderly manner, and with as little disruption as possible on each side.
"We want to make sure that Europe remains strong and prosperous and is capable of projecting its values, leading in the world, and defending itself from security threats.
"We want the United Kingdom, through a new deep and special partnership with a strong European Union, to play its full part in achieving these goals."
In the first sign of potential controversy, May said Britain believed it was "necessary" to negotiate the future trade deal alongside the divorce - something the EU does not agree with.
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