The letter signed by British Prime Minister Theresa May announcing that the UK intends to leave the EU under Article 50 has been handed to European Council President Donald Tusk in Brussels by UK permanent representative Tim Barrow.

It means Mrs May has launched divorce proceedings that will bring to an end a relationship of more than 40 years.

The prime minister signed the letter that starts the formal exit process last night and the historic document has now been delivered to EU chiefs.

It marks the start of complex and contentious negotiations that put the UK on course to break its ties with the bloc by the end of March 2019.

Mrs May urged the country to “come together” as she looks to heal the deep wounds caused by a referendum campaign that left the UK mired in division.

The PM’s top team gathered around the Cabinet table at No 10 this morning as she updated them on the content of the letter formally invoking Article 50.

Mrs May this afternoon delivered a statement on the triggering of Article 50 to the House of Commons:

This is an historic moment from which there can be no turning back. Britain is leaving the European Union.

“We are going to make our own decisions and our own laws, we are going to take control of the things that matter most to us, and we are going to take this opportunity to build a stronger, fairer Britain – a country that our children and grandchildren are proud to call home.

“That is our ambition and our opportunity,” she said.

Key EU figures agreed to enter into Brexit talks in a “positive spirit” during a series of telephone calls with Mrs May yesterday evening.

German Chancellor Angela Merkel, Mr Tusk and European Commission President Jean-Claude Juncker said the UK would remain a “close and committed ally”.

Within 48 hours, the European Commission is expected to issue “draft negotiation guidelines”, which will be sent to the 27 remaining states for consultation.

Their leaders will meet on 29 April at an extraordinary European Council summit to agree a mandate for chief negotiator Michel Barnier and clear the way for talks to begin in earnest in May.

The key point of contention as soon as Article 50 is triggered is the order in which different aspects of Brexit are approached.

Effectively, there are two issues to be settled – the terms of Britain’s withdrawal from the EU and arrangements for future trade relations.

On top of that is a possible third negotiation on a “transitional arrangement” covering the period between the moment of departure and new trade rules taking effect.

A white paper will tomorrow be produced on the Great Repeal Bill, the legislation that will turn four decades of EU regulations into domestic laws.