British Prime Minister Theresa May, left, and German Chancellor Angela Merkel discuss the next steps of Brexit in Berlin on July 20. (Adam Berry/Getty Images)

Almost 25 years ago, the Soviet Union crumbled under the weight of dissent within its 15 republics — including the largest, the Russian Federation. At the time, much of the West hailed the regime shift as the inevitable victory of the Anglo-European capitalist model of liberal economics and democratic governance.

But it’s very possible that in the early years of dissent, the Soviet regime retained its union by adopting a constitution of self-preservation — an approach Western leaders failed to replicate more recently, given Britain’s impending exit from the European Union.

Although Britain voted to leave the E.U. in late June, no one is quite sure when Downing Street will file the actual divorce papers. But there is a clear constitutional pathway to leave the E.U. — Article 50 of the Lisbon Treaty, which gives every E.U. member state the right to trigger its own withdrawal. There is some controversy surrounding whether an act of Parliament is needed to trigger Article 50 and start the formal process, but the provision itself is otherwise very clear.

When the draft of the E.U.’s Lisbon Treaty first came out in 2007, it was in essence a repetition of the E.U. Constitution that had been floated only two years before. Yet many experts at the time wondered why, if it believed in its mandate and vision for the economic and political union of nations, the E.U. would give member states the option of leaving.

Were the architects of the Lisbon Treaty incompetent?

Astonishingly, former European commissioner and Italian prime minister Giuliano Amato noted in July that Article 50 was never intended to be used. Amato, the author of Article 50, said the provision was there to placate Britain’s Euroskeptics. He and others had hoped to introduce a “safety valve” to release tension among the E.U. member states and allay fears that individual nations had no recourse to leave the bloc.

Article 50 is very detailed. It stipulates that countries seeking withdrawal must provide a formal notification to the E.U. Council; stresses when and how E.U. institutions will negotiate an agreement for withdrawal; and describes how the treaties of the E.U. shall cease to apply to the member state two years after the date of formal notification.

If Amato’s surprising announcement holds true, then Article 50 was the most meticulously planned fiction since the Allies deceived the Germans into believing the D-Day landings would take place at Pas-de-Calais. Why include detailed exit provisions if no member state was expected to go through with it?

The Soviets took an interesting approach

In hindsight, there was a far simpler option to achieve this deception — a clever trick modeled on Leonid Brezhnev’s Soviet Constitution of 1977. Article 72 of the Soviet Constitution made it clear that “each Republic shall retain the right freely to secede from the U.S.S.R.” Yet, initially there was no actual mechanism for any of the 15 Soviet republics to pack its bags and leave. Moscow adopted a legalistic line of argument as a last resort to preserve the U.S.S.R. as a superpower in the early 1990s.

As the Baltic republics began a wave of parliamentary votes and referendums for independence, the response came back from the Supreme Soviet that “while affirming the right of every union republic to freely leave the U.S.S.R. … until a law on the process of secession from the U.S.S.R. has been adopted, the resolutions of the Supreme Soviet [of the individual republics] … are contrary to Articles 74 and 75 … and are invalid.”

And here’s the legal conundrum: Article 74 stipulated that in case of discrepancies between the law of the USSR and the individual republics, the law of the U.S.S.R. would prevail (a supremacy clause that was effectively backed up with the Soviet arsenal of weaponry and tanks). Article 75 asserted that the sovereignty of the U.S.S.R. extended throughout its territory.

This is what many lawyers refer to as a “lacuna” — a gap or void in legal drafting. In the absence of a clear process for withdrawal, how can you bridge the gap between the right freely to secede and the overarching supremacy of the laws of the Soviet Union? Well, you don’t. You admit to the existence of the gap, hold up your hands, reiterate the supremacy of the laws of the U.S.S.R. and apologize for the inconvenience.

Of course, Brezhnev’s rule was never intended to be used either, and the vagueness of Article 72 was not enough to prevent the fracture of the Soviet Union. But crucially, the secession of national parliaments was not encouraged by the underlying constitutional settlement. as it is in the case of the E.U. Finally, in April 1990 the Supreme Soviet gave in. Published in the newspaper Pravda as a frantic attempt to respond to calls for independence, “The Law of the U.S.S.R. on the Procedures for Resolving Questions Related to the Secession of Union Republics from the U.S.S.R.” sought to legitimize an outcome that simply was not desired by those legislating for change.

What’s the lesson for the E.U. leadership, or for future global integration efforts?

In hindsight, it is really quite simple to achieve the facade that a nation might exercise its democratic right to self-determination. The solution is in the drafting: Just make sure that it can’t actually do so.

Of course, before drafting association agreements, treaties and codified constitutions, it might be far better to sit down with lawyers and include only those provisions that might realistically be relied upon. Otherwise, the result will be (as in the case of the E.U. and the Soviet Union) a constitution of political statement rather than one of real effect.

Paul Fisher is a British lawyer and former lecturer at St. Catherine’s College, University of Oxford. Follow him on Twitter @Paul3Edward.