The 1720 English financial bubble that burst amid the South Sea Company collapse was the South Sea Bubble.
The South Sea Company received rights connected to British trade with Spanish South America and offered to convert government debt into company shares. Investors drove the share price from about £128 in January 1720 to more than £1,000 by August, despite the company’s limited actual trading prospects.
Speculation spread to numerous new ventures, and Parliament passed the Bubble Act in June 1720 to restrict companies operating without a royal charter or parliamentary authorization. The law did not itself create the bubble, but its enforcement damaged confidence and helped intensify the reversal.
By December, South Sea shares had collapsed to roughly £124. Many investors were ruined, and the scandal damaged public trust in Parliament and finance. The contemporaneous Mississippi Bubble in France was a separate, though related, episode of speculative expansion.