European Council President Donald Tusk delivers a speech during a debate on the outcome of the last June 28-29 EU summit at the European Parliament in Strasbourg, France, July 3, 2018. REUTERS/Vincent Kessler/File Photo

BRUSSELS (Reuters) - European Council President Donald Tusk raised the idea that Brexit might be called off in a tweet on Monday after Boris Johnson, a campaigner for Britain to leave the EU, resigned as foreign secretary.

Echoing a comment he made to reporters after the earlier resignation of Brexit Secretary David Davis, Tusk tweeted: “Politicians come and go but the problems they have created for people remain. I can only regret that the idea of Brexit has not left with Davis and Johnson. But...who knows?”

Tusk, a former Polish prime minister, is overseeing the negotiations with London on its departure and has been highly critical of Brexit. He has said in the past that Britons would be welcome to change their minds and stay in the European Union.

Speaking to reporters earlier, Tusk said: “The mess caused by Brexit is the biggest problem in the history of the EU-UK relations and it is still very far from being solved, with or without Mr Davis.

“Unfortunately, the idea of Brexit has not left together with David Davis.”