Which London-based exchange experienced a record one-day percentage fall on Black Monday in 1987?

The London Stock Exchange experienced a record one-day percentage fall on Black Monday in 1987.

On October 19, 1987, the FTSE 100 index dropped 26.45 percent, one of the most dramatic falls recorded by a major national market. The decline followed severe selling in Hong Kong and other markets, then spread through Europe and North America. The episode demonstrated how quickly modern financial markets could transmit fear across borders.

The London crash was linked to several pressures, including concerns about overvalued shares, rising interest rates, currency tensions, and automated portfolio-insurance strategies. Investors also faced a highly interconnected market in which selling in one country could influence expectations elsewhere.

The FTSE 100 was launched in 1984 and became the best-known benchmark for large companies listed in London. The exchange itself is the London Stock Exchange, while the FTSE 100 is the index that measures leading eligible companies. Those two names are often confused when describing the 1987 event.