The Prime Minister has triggered Article 50 after her letter to European Council President Donald Tusk was delivered by Ambassador Sir Tim Barrow in Brussels.

Mr Tusk immediately responded on Twitter: "After nine months the UK has delivered. #Brexit."

Image: Sir Tim Barrow delivers the PM's Brexit letter to Donald Tusk

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Kicking off the two-year process of withdrawal from the European Union, Theresa May told MPs: "This is a historic moment from which there can be no turning back."

The PM accepted it was "a day of celebration for some and disappointment for others".


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But she added: "Now is the time for us to come together, to be united across this House and across this country to ensure that we work for the best possible deal for the UK and the best possible future for us all."

She pledged to deliver "the democratic will of the British people" and to take the "unique opportunity" to "shape a brighter future" for the UK, adding: "I choose to believe in Britain and that our best days lie ahead."

After nine months the UK has delivered. #Brexit — Donald Tusk (@eucopresident) March 29, 2017

Under the terms of the Lisbon Treaty, a two-year period of talks with the 27 remaining EU member states lies ahead.

After marking out hard lines on future payments to the European Union and the influence of EU law after Brexit, the text of the Prime Minister's letter offered some room for manoeuvre in negotiations.

Mrs May struck a note of conciliation, insisting: "We are leaving the European Union, but we are not leaving Europe - as we want to remain committed partners and allies to our friends across the continent."

But she said a UK exit without a deal "is not the outcome that either side should seek".

Image: Theresa May's letter informing the EU that Britain will be leaving runs to six pages. Continue through for the rest of the document /

Mr Tusk told a news conference shortly after being handed the Article 50 notice: "There is no reason to pretend that this is a happy day, neither in Brussels nor in London.

"After all most Europeans, including almost half the British voters, wish that we would stay together, not drift apart.

"But, paradoxically, there is also something positive in Brexit.

"Brexit has made us, the community of 27, more determined and more united than before."

And in a personal message to Britain he added: "We already miss you. Thank you and goodbye."

The European Commission, Council and Parliament have signalled that "EU law must apply until Brexit day" - when Britain officially leaves.

The European Parliament, which can veto a UK-EU deal, is next week expected to make the guarantee of full EU citizen rights a red line - a potential sticking point which Mrs May has highlighted as a "priority" for the talks ahead.

While Mrs May wants to negotiate a new trade deal with Europe alongside the divorce settlement, the EU has said it is reluctant to do so until after the UK has officially left.

Angela Merkel has rebuffed Mrs May's call for negotiations on Britain's withdrawal to run alongside talks on a trade deal.

The German Chancellor said: "The negotiations must first clarify how we will disentangle our interlinked relationship... and only when this question is dealt with, can we, hopefully soon after, begin talking about our future relationship."

The Commission chose the morning of the Article 50 declaration to formally block a key merger between the London Stock exchange and its German counterpart the Deutsche Borse.

Image: Theresa May leaves Downing Street on the day she triggered Article 50, beginning the two-year process of leaving the EU Image: Britain's EU ambassador Sir Tim Barrow arrives at the EU Council headquarters before serving notice of the UK's intention to leave Image: The Prime Minister announced in the House of Commons that she had triggered Article 50 at around 12.30pm Image: Brexit Secretary David Davis smiles after Mrs May's announcement Image: In response, Labour leader Jeremy Corbyn said the PM's Brexit plan was 'reckless and damaging' Image: Liberal Democrats leader Tim Farron accused Mrs May of 'leaping into the abyss' Image: Former Labour leader Ed Miliband asks a question after the announcement Image: Sir Tim Barrow delivers the Brexit letter to EU Council President Donald Tusk Image: Sir Tim leaves after delivering the six-page letter Image: Mr Tusk brandishes the letter at a news conference after receiving the document Image: A sombre looking Mr Tusk said: 'We already miss you. Thank you and goodbye.' Image: He said the invoking of Article 50 was not 'a happy day' for him, the EU, or for Britain /

Some influential commentators believe this decision was a key test of the EU's attitude to negotiations with the UK.

The pound pushed higher against the euro as the starting gun on Britain's formal exit from the EU was fired, climbing from a rise of 0.2% to 0.6% by the time the PM had finished addressing Parliament. There was little movement against the dollar.

"Today's the day the impossible dream came true. I'm delighted," former UKIP leader Nigel Farage told Sky News, while enjoying a pint in central London.

North of the English border, however, a day after MSPs backed a second Scottish independence vote, First Minister Nicola Sturgeon tweeted ahead of the declaration: "Today, the PM will take the UK over a cliff with no idea of the landing place. Scotland didn't vote for it and our voice has been ignored."