The Bank Holidays Act is a law in Great Britain that was first introduced in 1871. It established official public holidays or "bank holidays" throughout England, Wales, Scotland, and Northern Ireland.

Initially, the act designated four bank holidays: Easter Monday, Whit Monday, the first Monday in August, and Boxing Day (December 26th). In 1971, the act was amended to include a substitute holiday on the first Monday in May if May Day falls on a weekend.

Since then, there have been further additions to the list of bank holidays, including New Year's Day, Good Friday, May Day, the Spring Bank Holiday (the last Monday in May), the Summer Bank Holiday (the last Monday in August), and Christmas Day. In Scotland, there is also an additional bank holiday on January 2nd, known as "Hogmanay."

The idea of bank holidays in Great Britain can be traced back to the mid-19th century, when there was growing pressure for workers to be given time off for national and religious holidays. Prior to the Bank Holidays Act of 1871, there were no official public holidays in the United Kingdom, and any time off was at the discretion of individual employers.

The person most commonly credited with the idea of bank holidays is Sir John Lubbock, a Victorian banker, statesman, and naturalist. In 1871, Lubbock introduced a bill in the House of Commons that proposed the creation of four official public holidays. His proposal was motivated by a desire to give workers more leisure time and to promote social harmony by creating shared holidays for all classes of society.

The Bank Holidays Act was passed by Parliament on 2 June 1871, and the first official bank holidays were celebrated on August 5th of that year. The original four bank holidays were chosen because they were already popular holidays in many parts of the country, and they represented a mix of religious and secular occasions.

Over time, additional bank holidays were added to the calendar, reflecting changing cultural and political priorities. Today, bank holidays in Great Britain are an important part of the national calendar, and they continue to serve as opportunities for rest, relaxation, and celebration.

The purpose of bank holidays is to provide workers with time off to celebrate important occasions and to promote leisure activities, tourism, and commerce. Banks and many other businesses are closed on bank holidays, and public transportation may run on a reduced schedule.