George Martin said of this decision in The Beatles: Anthology: “I decided that the drums, which are really the backbone of a good rock group, didn’t give the boys enough support.
“They needed a good solid beat, and I said to Brian, ‘Look, it doesn’t matter what you do with the boys, but on record, nobody need know. I’m gonna use a hot drummer.’
“Brian [Epstein] said, ‘Okay, fine.’ I felt guilty because I felt maybe I was the catalyst that had changed his [Best’s] life…”
When John, Sir Paul and George Harrison realised the engineers wanted them to replace Pete with a session drummer for their upcoming recording session in September, they decided to permanently remove him from the group.