Peter Frase excerpts a fascinating bit of Witold Rybczynski's 1991 essay, "Waiting For The Weekend," which examined leisure in the 18th century:
It was not unusual for sporting events, fairs, and other celebrations to last several days. Since Sunday was always an official holiday, usually the days following were added on. This produced a regular custom of staying away from work on Monday, frequently doing so also on Tuesday, and then working long hours at the end of the week to catch up. Among some trades the Monday holiday achieved what amounted to an official status. Weavers and miners, for example, regularly took a holiday on the Monday after payday—which occurred weekly, on Friday or Saturday. This practice became so common that it was called “keeping Saint Monday.”
Saint Monday may have started as an individual preference for staying away from work—whether to relax, to recover from drunkenness, or both—but its popularity during the 1850s and 1860s was ensured by the enterprise of the leisure industry. During that period sporting events, such as horse races and cricket matches, often took place on Mondays, since their organizers knew that many working-class customers would be prepared to take the day off. And since many public events were prohibited on the Sabbath, Monday became the chief occasion for secular recreations. Attendance at botanical gardens and museums soared on Monday, which was also the day that ordinary people went to the theater and the dance hall, and the day that workingmen’s social clubs held their weekly meetings.