Although George Harrison had decided to leave the band on January 10 1969, the remainder of the band continued on the process of recording and filming at Twickenham Studios in London for at least two days afterwards.
On January 13 1969, The Beatles and girlfriends (minus George) arrive at Twickenham Studios and produced minimal results. They end up basically having luch and then rehearsing a bit of "Get Back" before calling it quits.
On January 14 1969, most of the early session has John Lennon sitting in Twickenham Studios during a CBC interview with a reporter (some clips from the interview can be seen in the documentary "Imagine: John Lennon". During this time, both Paul and Ringo are at the grand piano pounding away Jerry Lee style and this is capture on film and can be seen in the "Let It Be" film. Once the CBC interview is over, the three Beatles sit around and improvise on some titles such as: "Mean Mister Mustard" and "Watching Rainbows" among others. The cameras present caught some of the set being dismantled at the end of the day and it was decided to leave Twickenham and move to Apple Studios in order to appease George Harrison who would return to the band under this condition.