Which speculative bubble burst in London in 1720 after Parliament passed the Bubble Act?

The speculative bubble that burst in London in 1720 after Parliament passed the Bubble Act was the South Sea Bubble.

The South Sea Company received a monopoly over British trade with parts of Spanish South America, although the practical trading opportunities were far smaller than many investors imagined. The company promoted a plan to convert government debt into shares, and its price rose dramatically as investors expected enormous profits. Speculation spread beyond the company to many new ventures.

When confidence failed later in 1720, South Sea shares collapsed, ruining many investors and causing political scandal. Parliament passed the Bubble Act in June 1720, restricting the formation of joint-stock companies without a charter; it did not itself cause the entire collapse, which developed over months. The South Sea episode is often paired with France’s Mississippi Bubble, another major eighteenth-century speculative crisis.