Theresa May will trigger article 50, the formal mechanism for starting negotiations for Britain to leave the European Union, on Wednesday 29 March, the prime minister’s spokesman has confirmed.

The UK’s permanent representative to the European Union, Sir Tim Barrow, notified the EU on Monday morning that a letter should be expected on that date. The move will put the UK on course to leave the EU on the same date in 2019.

May, who was visiting Wales on Monday, intended to visit Northern Ireland and Scotland before the formal notification was sent by letter, Downing Street said.

Speaking during her visit to Swansea after the date was announced, May said: “I am very clear that I want to ensure we get the best possible deal for the United Kingdom that works for everyone across the United Kingdom and all parts of the UK when we enter these negotiations.

“I have set out my objectives. These include getting a good free trade deal. They include putting issues like continuing working together on issues like security at the core of what we are doing. We are going to be out there, negotiating hard, delivering on what the British people voted for.”

The Brexit secretary, David Davis, confirmed article 50 would be triggered next week, calling the process “the most important negotiation for this country in 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.”

The prime minister’s spokesman said Barrow had had a conversation with the office of the European council president, Donald Tusk, earlier on Monday to give the EU notice of the date.

“There will be a letter, [May] will notify President Tusk in writing, and the prime minister has already confirmed she will give a statement to parliament as well,” he said. “More details will be given in due course.”