In 1970, Allen Klein, manager of The Beatles, brought Spector to England. While producing John Lennon's hit solo single "Instant Karma!", which went to #3, Spector was invited by Lennon and George Harrison to take on the task of turning the Beatles abandoned "Get Back" recording sessions into a usable album. Spector went to work using many of his production techniques, making significant changes to the arrangements and sound of some songs. The resulting album, Let It Be, was a massive commercial success and topped the US and UK charts. The album also yielded the #1 single, "The Long and Winding Road". Although viewed as a major creative comeback for Spector, it may also have contributed to the contentious Beatles breakup, as Spector added what some[citation needed] considered inappropriate choir and orchestral arrangements to Lennon's "Across the Universe", and Harrison's "I Me Mine". His overdubbing of "The Long and Winding Road" infuriated its composer, Paul McCartney, especially since the work was allegedly completed without his knowledge and without any opportunity for him to assess the results. In 2003, McCartney spearheaded the release of Let It Be... Naked, which stripped the songs of Spector's input. Spector later stated that McCartney's complaints were "bullshit" and did not stop McCartney from accepting the "Best Musical Score" award at the 1971 Academy Awards for the Let It Be soundtrack.
However, both John Lennon and George Harrison were satisfied with the results, and Let It Be led to Spector co-producing albums with both ex-Beatles. For George Harrison's multi-platinum album All Things Must Pass (#1, 1970), Spector provided a cathedral-like sonic ambiance, complete with ornate orchestrations and gospel-like choirs. The LP yielded two major hits: "My Sweet Lord" (#1) and "What Is Life" (#10). That same year, Spector co-produced John Lennon's Plastic Ono Band (#6) album, which featured a very different, sparse and raw sound.
In 1971, Spector was named director of A&R for Apple Records. He held the post for only a year, but during that time he co-produced the single "Power to the People" with John Lennon (#11), as well as Lennon's chart-topping Imagine album. The album's title track, which hit #3 upon its release and #1 after Lennon's murder, is frequently considered to be one of the greatest pop songs of all time. With George Harrison, Spector co-produced Harrison's "Bangla-Desh" (a #23 hit) and wife Ronnie Spector's "Try Some, Buy Some" (which made it to #77). Also that year, Spector recorded the music for the #1 triple album The Concert For Bangla Desh. The album later won the "Album of the Year" award at the 1972 Grammys. Despite being recorded live, Spector used up to 44 microphones simultaneously while recording to create his trademark Wall of Sound.
Lennon retained Spector for the 1971 Christmas single "Happy Xmas (War Is Over)" and the poorly-reviewed 1972 album Some Time In New York City (#48). Similar to the unusual pattern of success that Spector's A Christmas Gift For You experienced, "Happy Xmas (War Is Over)" also stalled in sales upon its initial release, only later to become a fixture on radio station playlists during the holiday season. In 1973, Spector participated in the recording sessions for what would be Lennon's Rock 'n' Roll album (#6). It was during these sessions that Spector's relationship with Lennon ended; some versions claim that the producer suffered a breakdown in the studio, brandishing a gun and disappearing with the Rock 'n' Roll tapes, although Spector biographer Dave Thompson places most of the blame on the out-of-control behavior of Lennon and his entourage. After several months, Lennon retrieved the tapes and finished the album himself.