Theresa May has finally revealed that she will trigger Article 50 on March 29, launching the two-year countdown to Brexit.
The Prime Minister informed EU Council President Donald Tusk on Monday morning that she will invoke the Article, ending months of speculation on the matter.
A Downing Street spokesman said UK Ambassador to the EU Sir Tim Barrow had informed the President's office of Ms May's intention verbally.
He added that Number 10 now wants negotiations to "start promptly" - once the article is invoked it will be up to the EU to come back, with an early response expected within 48 hours.
Announcing the Article 50 date, the Downing Street spokesman said: "Earlier on this morning the UK’s permanent representative in the EU informed the office of Donald Tusk, that it’s the UK’s intention to trigger Article 50 on March 29."
The Prime Minister will deliver her letter triggering Article 50 to President Tusk on the Wednesday, and deliver a statement to the House of Commons announce the move. There was no further detail about exactly what the letter would say at this point.
Ms May spokesman went on: "After we trigger the 27 will agree their guidelines for negotiations and the Commission will deliver their negotiating mandate.
"President Tusk has said he expected there to be an initial response within 48 hours. We want negotiations to start promptly but it’s obviously right that the 27 have an opportunity to agree their position."
The invocation of the Lisbon Treaty article will formally begin Brexit negotiations, kicking off a two-year period during which the the and UK will try to agree the terms of Brexit and what relations will look like once Britain leaves.
The period can only be made longer by way of a unanimous vote of all European countries' governments. If no deal is reached by the end of the period, the UK will crash out of the EU with no deal and revert to World Trade Organisation rules.
Ms May has said she believes that "no deal is better than a bad deal".
If she meets here goal of completing negotiations within the two-year Article 50 period, then it will mean Britain leaves the EU on March 29 2019.
Brexit Secretary David Davis said: "Last June, the people of the UK made the historic decision to leave the EU. Next Wednesday, the Government will deliver on that decision and formally start the process by triggering Article 50.
"We are on the threshold of the most important negotiation for this country for a generation.
"The Government is clear in its aims: a deal that works for every nation and region of the UK and indeed for all of Europe – a new, positive partnership between the UK and our friends and allies in the European Union."
Notification comes 279 days after the referendum of June 23 last year delivered a 52 per cent to 48 per cent majority in favour of withdrawal.
Ms May, who was visiting Swansea on Monday, is expected to conduct visits in all four nations of the UK before notification takes place.
Shadow Brexit secretary Sir Keir Starmer accused Ms May of having failed to build a national consensus on Brexit adding that the UK is now "divided at home and isolated abroad".
He went on: "It is also extraordinary that the Prime Minister has failed to provide any certainty about her plans for Brexit or to prepare for the clear dangers of not reaching a deal with the EU.
"Labour will hold the Prime Minister to account all the way, and argue for a Brexit deal that puts jobs, the economy and living standards first."
Liberal Democrat leader Tim Farron, who is demanding a second referendum on when Ms May agrees terms with the EU, said: "Theresa May is embarking on an extreme and divisive Brexit. She has rushed this through without a plan, and without a clue.
"On the day Theresa May is travelling the country claiming she wants to bring the United Kingdom together, she lets it be known she is about to unleash division and bitterness."
Labour MP Pat McFadden, leading supporter of Open Britain, said: "As she enters talks with our European partners, it is up to the Prime Minister to deliver the deal that she and her ministers have promised. That means a trade agreement that gives us the “exact same benefits” as we have now on access to the European market.
"The Government has promised a Brexit deal that will not damage our economy and put jobs at risk. They need to meet the tests they have set themselves."