Theresa May will trigger the two year process of leaving the European Union on March 29, No 10 has announced.
Sir Tim Barrow, the UK's ambassador to the EU, formally notified the office of Donald Tusk, the EU Council president, with a letter on Monday morning.
On Wednesday next week Mrs May will formally notify Mr Tusk by writing him a letter and then giving a statement to MPs later in Parliament.
The Prime Minister’s official spokesman said: “There will be a letter. We have always been clear we would trigger by the end of March and we have met that timetable.”
The spokesman declined to comment at this stage on the contents of the letter nor on whether there would be any further documents published next week.
No 10 said it expected a response within 48 hours from Mr Tusk.
It comes after speculation that Mrs May was considering calling an election before 2020, the date when one is due under the Fixed-term Parliaments Act.
But the Prime Minister’s spokesman said: “There is no change on our position on an early general election.” Asked what that position is, she added: “That there isn’t going to be one.
“We have been clear there is not going to be an early general election. It is not going to happen.”
The spokesman said there was a fixed term parliament act and Mrs May was focused on “delivering the will of the British people”.
Mrs May revealed in the run-up to her first speech as Prime Minister at the Conservative Party conference that she would trigger Article 50 no later than the end of March 2017.
However, she was accused of “losing momentum” and “making errors” by delaying the formal start of Brexit talks in the wake of Nicola Sturgeon’s surprise demand for a Scottish independence referendum.
The Prime Minister was expected formally to start negotiations with other EU member states last week, after Parliament had passed a law allowing talks to begin.
Responding to the announcement, David Davis, the Secretary of State for Exiting the EU, 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."
What is Article 50?
The road ahead is unclear. No state has left the European Union before, and the rules for exit – contained in Article 50 of the Treaty of Lisbon – are brief.
The Lisbon Treaty, which became law in December 2009, is designed to make the EU "more democratic, more transparent and more efficient" and is an agreement signed by the heads of state and governments of countries that are EU members.
How long will it take?
The process is supposed to take two years but many people believe that it could take longer.
The timescale can be extended, but only by the unanimous consent of the European Council. So every other member state Government would have to agree.
Triggering Article 50, formally notifying the intention to withdraw, starts the clock running. After that, the Treaties that govern membership no longer apply to Britain.
The terms of exit will be negotiated between Britain’s 27 counterparts, and each will have a veto over the conditions.
It will also be subject to ratification in national parliaments, meaning, for example, that Belgian MPs could stymie the entire process.
Two vast negotiating teams will be created, far larger than those seen in the British renegotiation. The EU side is likely to be headed by one of the current Commissioners.
Untying Britain from the old membership is the easy bit. Harder would be agreeing a new trading relationship, establishing what tariffs and other barriers to entry are permitted, and agreeing on obligations such as free movement. Such a process, EU leaders claim, could take another five years.
Business leaders want the easiest terms possible, to prevent economic harm. But political leaders say the conditions will be brutal to discourage other states from following suit.
How could the UK create a new life outside of the EU quickly?
One option will be to simply recreate EU laws as British statute. But Civil Service insiders expect a new Brexit government to opt for something much more radical, and to use the opportunity of “throwing off the shackles” to re-regulate Britain.
It means that the Government would have to perform three acts simultaneously:
- Negotiate a new deal with Brussels
- Win a series of major bilateral trade deals around the world
- Revise its own governance as EU law recedes
Running the show would be an effective “Ministry for Brexit”, under a senior minister.
Officials expect the scrapping of EU law could result in an avalanche of new legislation in every corner of Whitehall – perhaps 25 Bills in every Queen’s Speech for a decade.
Hundreds of Treasury lawyers and experts would have to be hired for areas – such as health and safety, financial services and employment – where Britain had lost competence to Brussels. Meanwhile, a Trade Ministry will be required, with hundreds of new negotiators, to establish new deals around the world.