Black Wednesday: The Day Britain Left the ERM
On 16 September 1992 the Bank of England raised rates twice in a single day and still could not hold the pound inside its currency band. It left the system that evening.
The Arrangement
The Exchange Rate Mechanism required member currencies to trade within defined bands against each other. Britain joined in 1990 at a rate many economists considered too high.
A fixed or semi fixed exchange rate imposes a specific constraint. If the currency weakens toward the bottom of its band, the central bank must defend it, either by selling foreign reserves to buy its own currency or by raising interest rates to make holding that currency more attractive.
The Underlying Tension
Britain's problem was that domestic conditions and the defence requirement pointed in opposite directions. The economy was weak and needed lower rates. German rates were high following reunification spending, which pulled capital toward the mark and pressured everything else in the system.
So Britain was obliged to maintain high interest rates during a recession purely to defend a currency level, with no domestic economic justification for doing so.
Speculators were not betting the pound was overvalued. They were betting Britain would eventually choose its economy over the exchange rate, which is a bet about politics.
Why the Defence Could Not Hold
The asymmetry favours the attacker. A speculator selling the currency risks a modest loss if the peg holds, since the currency can only rise to the top of its band. If the peg breaks, the gain is large and immediate.
The defender faces the opposite. Holding the line costs reserves and imposes real economic damage continuously, and succeeding merely returns you to where you started.
On the day itself the Bank of England announced an increase from 10 to 12 percent, then announced a further rise to 15 percent that was never actually implemented. Announcing two increases in one day signals desperation rather than resolve, and the market read it that way.
The Trade
George Soros and his fund were the most prominent participants, reportedly earning around a billion dollars. The mechanics were straightforward: borrow sterling, sell it for marks, and repay in cheaper sterling after the devaluation.
The size mattered. A position large enough to exhaust the defender's reserves accelerates the outcome it predicts, which is why these episodes are described as self fulfilling once they gather sufficient scale.
The Aftermath Nobody Expected
The interesting postscript is that leaving the mechanism was economically beneficial. Freed from defending the rate, Britain cut interest rates substantially, the pound depreciated, exports became more competitive, and a sustained recovery followed.
The episode is sometimes called White Wednesday for that reason. The policy failure was joining at an unsustainable rate and defending it too long, rather than the exit itself.
The Bottom Line
Britain defended a rate its economy could not support, and speculators bet correctly that politics would eventually win. A fixed rate is only as credible as the domestic pain a government will accept to hold it.