The 1987 crash that caused the largest one-day percentage fall in the FTSE 100, when London shares dropped 26.45%, was Black Monday.
On October 19, 1987, stock markets around the world plunged. London’s FTSE 100 lost 26.45 percent, while the Dow Jones Industrial Average fell 22.6 percent, its largest one-day percentage decline. The selling followed weakness in international markets and was intensified by computerized trading strategies, portfolio insurance and investor fear.
Black Monday was a global market crash, not merely a Wall Street event. Trading systems, liquidity problems and a lack of coordinated circuit breakers contributed to the speed of the decline. The crash did not lead to a depression like the 1929 collapse; many markets eventually recovered, although the event permanently influenced market regulation and trading safeguards.