European Union and British Union flags are seen blowing in the wind in London, Britain, March 20, 2017. REUTERS/Toby Melville

BRUSSELS (Reuters) - The European Union’s 27 leaders will meet at the end of April to agree their negotiating lines for Brexit talks, after London sends in a formal notification that it wants to leave the EU on March 29th, three sources in Brussels said on Tuesday.

The meeting is a necessary step before the negotiations between Britain and the 27 remaining EU states can start formally.