The man who wrote Article 50 did not imagine his own country would be the one to use it.

Veteran British diplomat John Kerr — now Lord Kerr of Kinlochard — drafted the text that sets out the procedure for leaving the European Union as part of an effort to draw up an EU constitutional treaty in the early 2000s.

That initiative was scuppered by referendum defeats in France and the Netherlands but some elements ended up in the EU’s Lisbon Treaty, which came into force in 2009.

One of the sections pasted across became Article 50, which will be invoked by Prime Minister Theresa May on Wednesday when she notifies the EU that Britain intends to depart after more than 40 years of membership.

“I don’t feel guilty about inventing the mechanism. I feel very sad about the U.K. using it,” Kerr told POLITICO. “I didn’t think that the United Kingdom would use it.”

After a high-flying career in the Foreign Office that included assignments as Britain’s ambassador to Washington and to the EU, Kerr drew up the text as secretary-general of the European Convention, which was charged with writing the constitutional treaty in 2002 and 2003.

"It seemed to me very likely that a dictatorial regime would then, in high dudgeon, want to storm out" — Lord Kerr

At that time, the rise of Austrian far-right leader Jörg Haider was a big worry for mainstream EU leaders and some southern European EU members had returned to democracy only in recent decades. Kerr imagined that the exit procedure might be triggered after an authoritarian leader took power in a member country and the EU responded by suspending that country’s right to vote on EU decisions.

“It seemed to me very likely that a dictatorial regime would then, in high dudgeon, want to storm out. And to have a procedure for storming out seemed to be quite a sensible thing to do — to avoid the legal chaos of going with no agreement,” Kerr said.

Although he retired from the Foreign Office a decade and a half ago, Kerr remains active in public life. He spoke out against Brexit during last year’s referendum campaign and contributes to debates in the House of Lords.

He has argued publicly — and controversially — that Article 50 is not irrevocable. In other words, during the two-year negotiating period set out in the text, Britain could decide not to leave after all and simply remain an EU member. However, he says he cannot imagine how politics in Britain would allow such a U-turn.

Speaking by telephone from London, Kerr, a Scot in his mid-70s, displayed a sharp mind and dry wit. At one point, he correctly predicted his interviewer’s next question and he joked about his “beautiful prose” in Article 50 — a strictly colorless collection of about 260 words, split into five small sections.

Targeting Euroskeptics

Kerr took up the role as secretary-general to the European Convention, a body chaired by former French President Valéry Giscard d’Estaing, after retiring from the Foreign Office as its top civil servant.

He took a small flat in the picturesque Petit Sablon area of Brussels and set to work in an office at the back of the European Council’s Justus Lipsius building, leading two-dozen staff supporting the convention.

Kerr said he had favored setting out a formal departure procedure partly to undermine an argument made by British opponents of EU membership — even though, he said, their logic didn’t stack up.

“In Britain there was, among Euroskeptics, the theory that one was tied to one’s oar with no escape and rowing to the unknown destination of ever-closer union,” he said. “That Euroskeptic theory was always nonsense because you don’t need a secession article to secede. If you stop paying your subscription, stop attending the meetings, people would notice that you’d left.”

Kerr highlighted two key elements of Article 50 which could play a big role in the negotiations to come.

The process outlined in the text is, he noted, “about divorce … about paying the bills, settling one’s commitments, dealing with acquired rights, thinking about the pensions. It’s not an article about the future relationship.”

However, the article also states that the divorce deal should take account of the “framework” of the future relationship between the EU and the departing country. Kerr said a full agreement covering trade and all other aspects of relations between Britain and the EU could not possibly be concluded in two years but a framework would have to be negotiated.

“Don’t ask me what that framework looks like. Is that another treaty? Is it a European Council Conclusions text? I don’t know what the framework will be but … unless it exists, then the divorce settlement, if there is one, is legally vulnerable — because in order to be ‘taken into account,’ it has to exist,” he said.

That meant, Kerr said, that discussions about the divorce and about the outline of the future relationship would have to take place in parallel.

“I don’t believe that it will be possible for the Commission to insist — and I’m not convinced that they will try to insist — that the money has to be all tied up before one can talk about anything else," he said. "If I were the British negotiators, I would go clutching this article in my hand and say ‘But hang on, we have to have a framework.’”

Rules of the game

Article 50 has been the subject of fierce debate since the Brexit referendum, including in the U.K. Supreme Court. But Kerr said it caused little fuss when it was discussed as part of the European Convention.

“There were plenty of articles which caused tremendous debate. This was not one of them,” he said.

In the Supreme Court case over whether the U.K. parliament had to give its approval before the government could invoke Article 50, both the government and their opponents contended that this notification could not be withdrawn. But Kerr said the view was different on the Continent.

"I would love to be the British negotiator who came with the second letter saying ‘actually we’ve changed our mind’" — Lord Kerr

“I think if you ask an EU lawyer, he will tell you straight away that of course it’s not irrevocable,” he said. “And if the issue was decided in a court, it would be decided in the European Court of Justice and it would be found that it is not irrevocable.”

He added: “The rules of the game in the EU are that you can change your mind. Many a member state has changed its mind during a legislative procedure because it’s had a general election back home and the left has thrown out the right or the right has thrown out the left and it’s stood on its head in the [European] Council — and that’s accepted.”

He said he could not see the British government deciding to reverse course. “But there is no doubt that if they did go in that direction — if the deal looked so bad that the government was thrown out or decided that it could not recommend it — then it would be perfectly possible to carry on,” he said.

Although there would be no legal price to pay under that scenario, Kerr said, other EU members would probably extract some kind of political concession from Britain — but it might not be too severe. He said they would not be able to touch Britain’s legally enshrined rebate from the EU budget, for example.

Kerr said he would be “pontificating in the Lords” on Wednesday when May sends her notification to the EU. His days on the diplomatic front lines may be behind him but he would relish one last big mission — heading back to Brussels with a note from the British government saying it had decided not to go ahead with Brexit, bolstered by his own handiwork in the form of Article 50.

“This is a little unlikely,” he said, pausing for a brief chuckle, “but I would love to be the British negotiator who came with the second letter saying ‘actually we’ve changed our mind’ because I would come surrounded by lawyers and every time somebody raised a price that I would have to pay, I would say ‘please consult your lawyer, I don’t have to pay any price, I’m here by right.’”

Click here for an interactive guide to Article 50 with comments from Lord Kerr.