The speculative bubble surrounding Britain’s South Sea Company in 1720 was called the South Sea Bubble.
The South Sea Company was founded in 1711 and received a government-supported monopoly over British trade with Spanish South America, although its realistic trading opportunities were limited. In 1720, Parliament approved a plan for the company to assume part of the national debt, encouraging investors to buy its shares.
Share prices rose dramatically as promoters spread optimistic claims and investors joined the speculation. The company’s stock reached about £1,000 in August 1720 before confidence collapsed. Prices then plunged, ruining many investors and producing political scandal in Britain.
The South Sea Bubble was part of a wider European speculative episode. France’s Mississippi Bubble collapsed at about the same time, under the system associated with John Law. The two events are related but are separate bubbles, so the South Sea Bubble is the specific answer for Britain’s crisis.