"Knees Up Mother Brown" is a song, published in 1938, by which time it had already been known for some years.

The song dates back to at least 1918 and appears to have been sung widely in London on 11 November of that year, Armistice Night, at the end of the First World War.[1] The 1938 version was attributed to Bert Lee, Harris Weston and I. Taylor.

The song became popular in English public houses and was particularly associated with Cockney culture. During the Second World War it was performed frequently by Elsie and Doris Waters. It was also later performed on television by Noel Harrison and Petula Clark singing as a duo.

The expression "knees up" came to mean a party or a dance. Originally, the phrase referred to the position of a woman in sexual intercourse.

In the 1964 Disney film Mary Poppins the song "Step in Time" written by the Sherman Brothers was based on Knees Up Mother Brown.[6] According to Richard Sherman, the Knees Up Mother Brown dance was taught to Walt Disney, Tony Walton, and others by Peter Ellenshaw (the Disney Studio's head of special effects) and the Sherman Brothers witnessed them doing the dance and got the idea for "Step in Time"

In 1965 Bing Crosby and Rosemary Clooney sang an updated version on their album That Travelin' Two-Beat.

On the 1971 Monty Python album Another Monty Python Record, the song is described as one of the "folk songs of the Spanish Inquisition." As performed by Cardinals Ximénez (Michael Palin), Biggles (Terry Jones), and Fang (Terry Gilliam), the lyrics are altered to "Knees upon the ground" and it closes out the album's last track.

In 1980 Fozzie Bear performed this song in an episode of The Muppet Show with his mother, Emily, portraying "Mother Brown."

In her 1983 television concert special filmed at London's Dominion Theatre, Dolly Parton is shown singing the song with a group of men in a pub during the opening credits.

In the 1986 movie Sweet Liberty, Michael Caine's character, Elliot James, recounts a tale of singing "Knees Up Mother Brown" on the streets of London during World War II. He runs into Winston Churchill, who joins in the singing.

In the 1999 movie "The Talented Mr Ripley", Jack Davenport's character, Peter attempts to cheer up Tom (played by Matt Damon) by playing a bit of the tune on the piano.

A version with ribald lyrics playing off the "blackout" regulations in WWII-era London is quoted both in Ken Follet's book Eye of the Needle (1978) and Laura Wilson's The Lover (2004).

In Season5 Episode10 of Frasier, the crowd at Daphne's pub, the Fox and Whistle, requests 'Knees Up Mother Brown' from the piano player.
In association football
The song could often be heard sung on match days at the Boleyn Ground by fans of West Ham United Football Club and an unofficial (not officially run or moderated by the club) fan's internet forum takes it name from the song. It has also been adopted by fans of other football clubs for various chants, most recognisably with the words "Who Ate All the Pies?