On which date did the United Kingdom’s FTSE 100 suffer its largest one-day percentage fall?

The United Kingdom’s FTSE 100 suffered its largest one-day percentage fall on October 20, 1987.

The index dropped 26.45% during the global market turmoil surrounding Black Monday. The United States crash occurred on October 19, but British trading took place the following day because of the time difference. The FTSE’s collapse showed how quickly financial panic could cross national markets.

The 1987 episode affected exchanges across Asia, Europe, and North America. Investors worried about valuations, interest rates, currency tensions, and the effects of computerized trading systems. Although the losses were extreme, the global economy did not experience a repeat of the 1930s Great Depression.

The date is sometimes confused with October 19, the day of the record Dow decline in New York. Both dates belong to the same international crash, but they describe different markets and trading sessions.