Brexit countdown: UK formally pitches itself into the unknown

British prime minister Theresa May will file formal Brexit divorce papers today, pitching the UK into the unknown and triggering years of uncertain negotiations that will test the endurance of Ireland and the EU.

Nine months after Britons voted to leave, Ms May will notify EU Council president Donald Tusk in a letter that the UK really is quitting the club it joined in 1973.

Ms May, an initial opponent of Brexit who won the top job in the political turmoil after the referendum vote, will then have two years to settle the terms of the divorce before it comes into effect in late March 2019.