In an interview with the BBC, Scottish Lord Kerr of Kinlochard also said the process “wasn’t really necessary” as it has always been possible for a country to withdraw.
He added: “If you stopped paying the bills and you stopped turning up at the meetings, in due course your friends would notice that you seemed to have left.”
Lord Kerr, who as well as serving as UK ambassador to the EU and USA is a former head of the British diplomatic service, made the remarks ahead of a High Court ruling on the triggering of Article 50 due this morning.
He said: “I thought the circumstances in which it would be used, if ever, would be when there was a coup in a member state and the EU suspended that country’s membership.
“I thought that at that point the dictator in question might be so cross that he’d say ‘right, I’m off’ and it would be good to have a procedure under which he could leave.”
Lord Kerr also said Brexit was “not irrecoverable” and the UK might want to reconsider once the full terms become apparent.
He added: “You can change your mind while the process is going on.
“During that period, if a country were to decide actually we don’t want to leave after all, everybody would be very cross about it being a waste of time.
“They might try to extract a political price but legally they couldn’t insist that you leave.”
The High Court ruling due today is one of the most important constitutional cases in generations.
Opponents argue the prime minister cannot use royal prerogative to trigger Article 50 of the Lisbon Treaty and start the UK’s exit from the European Union without the prior authority of Parliament.
Government lawyers say prerogative powers are a legitimate way to give effect “to the will of the people” who voted by a clear majority to opt for Brexit in the June EU referendum, reports the Press Association.
Following a three-day hearing in October the Lord Chief Justice, Lord Thomas - sitting with the Master of the Rolls, Sir Terence Etherton, and Lord Justice Sales - will give their ruling in a historic case expected to go to the Supreme Court for a final decision.
Theresa May announced at the Conservative Party conference that she intends giving an Article 50 notification by the end of March 2017.
Her opponents are drawn from all walks of life and led by investment fund manager and philanthropist Gina Miller.
Their teams of lawyers argued at the hearing in London that May unlawfully intended to by-pass parliamentary scrutiny while taking irreversible steps to remove statutory rights granted to UK citizens under the European Communities Act 1972, which made EU law part of UK law.
But the country’s top legal officer, Attorney General Jeremy Wright QC, said parliamentary consent for Article 50 was not required following the clear public referendum vote in favour of Brexit.
The Government was seeking “to give effect to the will of the people” and that was “wholly within the expectation of Parliament”, he said as he appeared on behalf of Brexit Secretary David Davis.
James Eadie QC, another senior member of the Government legal team, said any new treaty agreement with the European Union following Brexit would “very likely” have to be ratified by Parliament.
In submissions that caused the pound to rally, Eadie said the “view at the moment” was that ratification was likely if the royal prerogative was used to launch the Brexit process.
An Article 50 notification would only “fire the starting gun” for an expected two years of negotiations and not of itself change any common law or statutory right enjoyed by citizens.
Eadie added: “Any such changes are a matter for future negotiations, Parliamentary scrutiny, and implementation by legislation.”