She will move Article 50 of the Lisbon Treaty and make a statement in the House of Commons on March 29, finally setting in train Britain’s formal departure from the European Union.
The historic start of the process, 44 years after the UK joined the EEC in 1973, will trigger a two-year countdown for negotiations over the exit terms and any interim trade deal.
Brexit will take place by March 29 2019 at the latest, No 10 confirmed.
The UK’s permanent representative in Brussels, Sir Tim Barrow, this morning notified European Council president Donald Tusk that the Prime Minister has chosen Wednesday March 29 as the day to obey the instructions of the British people given in last June’s in-out referendum.
“We want negotiations to start promptly,” said the Prime Minister’s offcial spokesman this morning.
Asked if that would mean Brexit happening by March 29 2019, the PM’s spokesman said: “We have said we expect this to be a two-year process and we are confident that is what we will achieve.”
The starting move will be a hand-delivered letter from Mrs May to Mr Tusk, launching the exit procedures set out in the Lisbon Treaty. Mr Tusk said recently that EU leaders would respond within “more or less 48 hours” of the letter, starting possibly the most complicated series of negotiations in British history.
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.”
Mrs May’s spokesman appeared to rule out an early general election at the same time as revealing the date of Brexit, saying: “There is not going to be one.”
The date means Mrs May will have met her conference pledge to trigger Brexit by the end of March by just two days.
Preparations are understood to be highly advanced, with the letter to Mrs Tusk already drafted and Britain’s opening demands in the Brexit negotiation prepared.
The Prime Minister was in Wales today on a pre-Brexit tour of the UK designed to show she is listening to the views of every region.
March 29 is anti-Brexit campaigner Sir John Major’s 74th birthday - and the wedding anniversary of fellow Remain campaigner and ex-PM Tony Blair.