Sellers had a casual on-and-off association with The Beatles. George Harrison met Ravi Shankar at Sellers' house, changing the course of Harrison's musical and spiritual explorations. (Shankar advised Sellers on playing the sitar in The Party.) In 1968, during his two-week hiatus from the Beatles during the White Album recordings, Ringo wrote "Octopus's Garden" while vacationing with his family in Sardinia on Sellers' yacht. Starr also gave Sellers a rough mix of songs from the White Album, and here's a video of Sellers paying the Beatles a visit during the "Get Back" sessions.
He performed a number of humorous covers of Beatles songs, including a version of "She Loves You" as Dr. Strangelove. In that vein, here's a video from a December 1965 Granada ITV special, The Music of Lennon and McCartney. Sellers' cover of the Beatles' "A Hard Day's Night" — sending up Laurence Olivier's Richard III in the bargain — became a UK Top 20 hit that year.
Happily, and rather miraculously, we also have an outtakes reel: