Britain will formally begin Brexit by triggering Article 50 of the EU’s Lisbon Treaty on March 29, officials said on Monday, nine months after Britain voted to leave the European Union.

“We want the negotiations to start promptly,” Prime Minister Theresa May’s spokesman told reporters.

Britain’s envoy to Brussels Tim Barrow “has this morning informed the office of European Council President Donald Tusk of the UK’s intention to invoke Article 50 of the Lisbon Treaty on March 29,” the Brexit ministry said in a statement.

“Next Wednesday, the government will deliver on that decision and formally start the process by triggering Article 50,” he said.

“We are on the threshold of the most important negotiation for this country for a generation.”

Britain voted by a 52 percent majority to leave the European Union — the first member state ever to do so.

The divorce process under Article 50 gives a two-year framework for negotiations.

May has said she wants to leave the European single market in order to be able to control immigration.

The European Commission is expected to provide an initial answer to Britain’s Article 50 notification within 48 hours but negotiations are not expected to start for several weeks or even months.