The FT 30 index fell 73% during the 1973–1974 UK stock market crash.
The FT 30 was the London market's leading share index before the FTSE 100 replaced it in 1984. Its collapse was especially severe compared with the losses recorded by major U.S. indexes during the same global bear market. The FT 30's definitive low came in early January 1975, when it closed at 146 after an intraday nadir of 145.8.
The downturn was driven by several overlapping shocks. The collapse of the Bretton Woods monetary system and the 1971 Nixon Shock destabilized international finance, while the 1973 oil crisis sharply increased energy costs. Britain also faced inflation, recession, industrial unrest and a property and banking crisis.
The 73% figure refers to the index's peak-to-trough loss, not a single trading day. It is also not the decline of the later FTSE 100, which did not yet exist. Because the FT 30 represented only 30 companies, its performance should not be treated as a perfect measure of every UK investment.