Can a country leave the EU – and what does it cost?

Yes – Article 50 of the EU treaty gives every member the right to leave. Britain used it; the bill is still being counted.

The EU is, on this point, unusual among unions: exit is legal, written down, and tested once. Both facts – the open door and the price of walking through it – deserve plain statement.

The mechanics

Since 2009, Article 50 of the Treaty on European Union has provided a formal exit. The process: a member notifies the European Council of its intention; a two-year window opens to negotiate a withdrawal agreement (approved by qualified majority plus the European Parliament – the leaver needs no one’s permission to go); when the window closes, treaties simply cease to apply, deal or no deal. Extensions require all remaining members to agree unanimously.

Before 2020, the clause had never been used by a full member. Greenland – an autonomous territory of Denmark, not a member state – negotiated out in 1985 over fish; Algeria exited by becoming independent of France in 1962. The United Kingdom is the only country to have done the real thing: referendum June 2016, notification March 2017, three extensions, departure on 31 January 2020.

So the door exists and it opens. The interesting question is what’s on the other side.

The one case study

Britain entered the experiment as close to a best case as a leaver gets: a large G7 economy, its own globally traded currency, London’s financial machine, and deep trade relationships to fall back on. Six years of measured results, from sources with no stake in the referendum:

• The UK’s own fiscal watchdog, the OBR, builds its forecasts on Brexit reducing long-run productivity by 4 % and trade intensity by 15 % relative to remaining – assumptions it reviewed in 2025 and kept.
• An NBER study published this year puts GDP per capita 6–8 % below the remain counterfactual by 2025, with investment down 12–18 % and employment down 3–4 %.
• Goldman Sachs’ ten-year retrospective lands in the same 6–8 % range; NIESR projects 5–6 % by 2035.

For scale: a 6 % GDP shortfall is roughly the UK’s entire annual defense and education budgets combined, recurring. No serious estimate finds a net gain; the argument among economists is between “significant” and “very significant.”

What the leaver got – stated fairly

Britain regained its trade policy and used it (CPTPP accession, bilateral deals). It ended free movement and redesigned migration on its own terms – intake, notably, went up, but under British rules. It stopped paying into the EU budget, a real if modest saving of roughly a quarter-percent of GDP. And it holds formal regulatory freedom, exercised sparingly for a structural reason worth understanding: when your largest market writes rules for 450 million people next door, diverging from them costs you twice – once in lost access, once in duplicated compliance. Sovereignty on paper met the gravity of scale in practice.

That is the honest ledger: real symbolic and legal gains, purchased at a measurable, compounding economic price – paid mostly by people who were promised the opposite.

What it means for everyone else

Brexit settled an argument the EU could never settle about itself. Exit is not a hostage situation – the door works, the union survived a G7 economy’s departure intact, and no member has moved toward the door since. Polling across the continent shifted notably pro-membership after 2016, and in Britain, consistent majorities now tell pollsters the decision was wrong. The one tested answer to “can a country leave?” turned out to be: yes, freely – and the price tag is now public knowledge, which may be the most consequential thing the experiment produced. Whether the remaining members draw closer together is the sequel currently being negotiated.

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