What name is given to the day in 1992 when Britain pulled out of the European Exchange Rate Mechanism?

Black Wednesday occurred in the United Kingdom on 16 September 1992, when John Major's Conservative government was forced to withdraw the pound sterling from the European Exchange Rate Mechanism (ERM) after it was unable to keep the pound above its agreed lower limit in the ERM. In 1997, the UK Treasury estimated the cost of Black Wednesday at £3.4 billion. In 2005, documents released under the Freedom of Information Act revealed that the actual cost may have been slightly less, £3.3 billion. Until the United Kingdom's decision to leave the European Union in June 2016 it was the most significant event to happen during its time as a member of the European Union and was made even more embarrassing as the United Kingdom was holding the Presidency of the European Communities at the same time.

The trading losses in August and September were estimated at £800 million, but the main loss to taxpayers arose because devaluation could have made them a profit. The papers show that if the government had maintained $24 billion foreign currency reserves and the pound had fallen by the same amount, the UK would have made a £2.4 billion profit on the pound sterling's devaluation.