Britain's envoy to the European Union, Tim Barrow, has hand-delivered the letter personally signed by U.K. Prime Minister Theresa May to EU Council President Donald Tusk notifying the EU of the U.K.'s intention to leave the bloc, thus officially triggering Article 50. The letter was delivered to and accepted by Tusk at approximately 1:20 p.m. local time in Brussels (12:20 p.m. in London).
The triggering of Article 50 means the clock is now ticking on the U.K.'s withdrawal from the EU. Its withdrawal must be fully agreed upon and ratified by all remaining 27 EU countries by 12:20 p.m. London time on March 29, 2019. If no agreement can be reached on the terms of the U.K.'s withdrawal by then, the U.K. will automatically be ejected from the EU and fall back on WTO trade rules unless the EU agrees to throw it a lifeline by giving it a transitional arrangement as negotiations continue.