In 1780, England’s Parliament passed a law to remove some of the restrictions against Roman Catholics. The one the government was most interested was to remove the restrictions to serving in the army. As the country was then involved in the American Revolution and wars against France and Spain, they needed all the recruits they could get.
Lord George Gordon was the leader of a Protestant Political Group and called on Protestants to protest to Parliament. Things got out of hand, and the riots lasted for days and devolved from politics to anti-Catholic pogroms and general looting and destruction. The troops put it down after some days at the cost of several hundred shot.
Gordon was put on trial for treason for inciting the mob. There were suspicions that the riots were part of some plot by the countries England was at war with, which proved unfounded.
In the end, Gordon was acquitted of treason. He remained controversial, eventually being convicted of libel against Queen Marie Antoinette. He fled to the continent to avoid prison, but oddly enough later returned and converted to Judaism. Eventually he was detected and died in prison.