The treaty clause that triggers exit from the European Union was not actually designed to be used, its author has said.

Giuliano Amato, a former prime minister of Italy, who later worked with the European Commission, helped draft the European Constitution, which became the Lisbon Treaty.

He said he had written the now infamous Article 50 but that it was largely for show.

“I wrote Article 50, so I know it well,” Mr Amato told a conference in Rome, according to Reuters.

He told the meeting he had specifically inserted the article to prevent the British government complaining there was no way for them to leave the bloc.

“My intention was that it should be a classic safety valve that was there, but never used. It is like having a fire extinguisher that should never have to be used. Instead, the fire happened.”

Mr Amato went on to describe Brexit as a "disaster", called David Cameron "mad" for calling a referendum over it and urged other countries not to follow suit.

Of impending talks, he said: "Don't give Britain the possibility of thinking that Brexit is a better way of doing what they have always done, grabbing what suits them [in the EU] and opting out of what they don't like. Brexit is a total opting out. They know this very well.

What is Article 50?

"The more they realise that they are losing, then the more chance there is that in 2020 [when there will be a general election] someone will do something about it."

He conceded that this was an "absurd hope" however, and as such wants "the negotiations [to be] dragged on so they won't be wrapped up by 2020. (Prime Minister) May wants to wrap things up by 2019, but it will be easy to prolong matters."

There has been speculation about when and how Article 50 will be triggered, prompting the start of exit negotiations.

Ms May has signalled that the clause will not be invoked until 2017. She has also said it will not be used until Scotland's position in negotiations is clear.

Patrick McLoughlin, the Tory chairman, said the process would be started before the next general election, but gave no further details.