German Chancellor Angela Merkel, French President Francois Hollande and Italy's Prime Minister Matteo Renzi | John Macdougall/AFP via Getty Images Germany, France and Italy say UK must launch Brexit process The EU’s remaining three biggest nations insist the UK must invoke Article 50 for Brexit negotiations to start.

BERLIN — The leaders of Germany, France and Italy jointly demanded Monday that Britain should formally launch the process for exiting the European Union before any negotiations on the terms of the divorce can take place.

Speaking in Berlin alongside French President François Hollande and Italian Prime Minister Matteo Renzi, Chancellor Angela Merkel said they had all "agreed that there will be no informal or formal talks about an exit of Great Britain until a request has been submitted to the European Council."

"We don’t want this to turn into a never-ending story,” Merkel added.

Britain has to invoke Article 50 of the Lisbon Treaty to formalize its departure, but Brexit campaigners would like informal negotiations before the official process begins. Merkel had signaled willingness to give Britain "a reasonable period of time," but insisted on Monday — ahead of an EU leaders' summit in Brussels on Tuesday — that Article 50 should come first.