Boris Johnson has torn up the Northern Irish backstop and demanded new terms for the UK to leave the EU with a deal in 10 weeks’ time.

In a letter to the EU on Monday he said the backstop was “anti-democratic and inconsistent with the sovereignty of the UK” and it risked “weakening the delicate balance embodied in the Belfast (Good Friday) Agreement”.

He said: “The backstop cannot form part of an agreed Withdrawal Agreement. That is a fact that we must both acknowledge.” He proposed replacing the backstop with “flexible and creative” arrangements to manage a soft border between Ireland and Northern Ireland after Brexit.

It came after a one-hour phone call in which the Prime Minister and Leo Varadkar, the Irish premier, clashed over the backstop.

Mr Johnson heads to Berlin on Wednesday for dinner with Angela Merkel, the German chancellor, before lunch in Paris with Emmanuel Macron, the French president, the following day, to persuade them both to agree that the EU should remove the backstop.

The week ends with Mr Johnson’s first appearance on the global stage when he represents Britain at the G7 meeting of world leaders in Biarritz in the south of France.

Mr Johnson has made the removal of the backstop – which will keep the UK in a customs union and the single market after Brexit until a solution is found to prevent a hard border – a central part of his plans to take the UK out of the EU by Oct 31.

In his letter to Donald Tusk, the EU Council president, he said he could not endorse “full alignment with wide areas of the single market and customs union” after Brexit. “That cannot be the basis for the future relationship and it is not a basis for the sound governance of Northern Ireland.”

He told Mr Tusk both the UK and EU should agree neither side “will put in infrastructure, checks or controls at the border” and said the backstop should be replaced” with “alternative arrangements” north and south to allow the sides to monitor movements of goods and people without a hard border.

The majority of MPs would agree to a deal without the backstop, he said, adding Parliament could act rapidly if it reached “a satisfactory agreement that did not contain the backstop.”