(AP) – The head of the European Council says the European Union must wait for the British government to decide whether to leave the bloc or stay in it.

Donald Tusk says Thursday that the European Treaty puts no pressure on a nation filing the Article 50 motion to leave the group at any certain time. He says until Britain files the motion, it remains a full EU member.

Tusk said on Polish TVN24 that “the European Union must wait for the British government to decide whether it wants to leave the union or whether it wants to stay in it.”

Tusk called Britain’s June 23 vote to leave the 28-nation bloc a “very sad thing” and said it was a “very serious mistake” of Britain’s political elite to call such a vote.