The speculative bubble that burst in London in 1720 was the South Sea Bubble.
The South Sea Company received special trading privileges and took on part of the British government's debt. Investors were attracted by promotional claims about the company's commercial prospects, especially its expected trade with Spanish-controlled areas of the Americas. Its shares rose dramatically as speculation spread through British society.
The price surge was not supported by the company's actual trading results. When confidence weakened, investors rushed to sell, causing the share price to collapse. The resulting financial crisis damaged many investors and led to parliamentary investigations, exposing corruption and insider dealing.
The South Sea Bubble is often discussed alongside France's Mississippi Bubble, which also collapsed in 1720. They were separate schemes, although both demonstrate how easy credit, public excitement, and unrealistic expectations can inflate asset prices far beyond underlying value.