A television screen displays an image of British Prime Minister Theresa May as she speaks during Prime Minister's Questions in the Houses of Parliament following the triggering of Article 50 of the Lisbon Treaty to begin the process of Britain's withdrawl from the European Union (EU), as man drinks a pint of beer inside the The Black Bull pub in Edinburgh, on March 29, 2017.
Britain and the European Union must 'work hard' to avoid a failure in Brexit negotiations, Prime Minister Theresa May said in the letter formally launching the process, calling it a 'momentous' challenge. May also called for talks on Britain's exit and on future trade ties to be worked out 'alongside' each other, although the EU has said the new trading relationship should only be discussed after Brexit is agreed. / AFP PHOTO / Andy Buchanan        (Photo credit should read ANDY BUCHANAN/AFP/Getty Images)