"Of course, the door is always open as long as the negotiations on Brexit have not finished," he said.

But he also warned at the time that that once the negotiations started, "it will be more and more difficult to go backwards".

Today, the French president took a swipe at staging referendums, such as the UK one on EU membership, saying: "We mustn't fall into the trap of the populists and extremes which consists of saying: 'Let's pose directly the question yes or no in a simplistic way, the response is always no."

He also said that Britain's political class had "lost the people" on Europe by failing to defend it as an idea, and simply selling it as a competitive space.

To avoid "binary" responses, a "vast debate" must ensue, with six months of "democratic conventions to identify the priorities, the preoccupations" of Europeans to build a "road map" for its future. These would feed debate ahead of the Brexit deadline and European parliamentary elections in 2019.