It began with the simple stroke of a pen. Donald Trump was fresh from lunch with Theresa May. Buoyant in his new role, the president kept the menu card to prove he had eaten with the British Prime Minister.

Arriving at the Pentagon, Mr Trump took the seat behind the executive desk, and at 4.42pm on Friday signed the document that was to prove the most explosive of his first week in office.

The executive order suspended entry of all refugees for 120 days and barred those fleeing the slaughter in Syria indefinitely. And it blocked entry into the United States for some three months for citizens of seven Muslim-majority countries.

The order, which the White House described as strict new measures to prevent terror attacks on US soil, was to go into immediate effect.