That begins two years of negotiations – although the process could be extended if Britain and all other EU countries unanimously agree.

In a BBC interview ahead of a speech to the annual conference of her ruling Conservative Party, she said: “I have been saying that we wouldn’t trigger it before the end of this year so that we get some preparation in place.

“I will be saying in my speech today that we will trigger [Article 50] before the end of March next year.”