THERESA MAY is to officially notify the European Union next Wednesday (March 29) that the UK is leaving.
Downing Street has said May would write a letter to the EU's 27 other members, and expected negotiations to begin as quickly as possible.
Talks on the terms of the departure and future relations with the bloc are not allowed until the UK formally tells the EU it is leaving.
The rights of both EU and British expatriates are believed to be among the first issues to be tackled during negotiations.
Mrs May is expected to make a statement to the House of Commons shortly after invoking Article 50.