[DeluxeMoustache]

Interesting. Wikipedia for Hey Jude says

In the song's final bridge section, at 2:58, the spoken phrase "####ing hell!" appears, uttered by Lennon. Scott admits that although he was told about it, he could not hear the words originally. Malcolm Toft, the mix engineer on the Trident recording, recalled that Lennon was overdubbing his harmony vocal when, in reaction to the volume being too loud in his headphones, he first called out "Whoa!" then, two seconds later, swore as he pulled the headphones off.

Then there is another account here that claims it was Paul
https://www.buzzfeednews.com/article...o-famous-songs

About halfway through "Hey Jude," there seems to be a "whoa" sound followed by somebody saying "####ing hell." Geoff Emerick, The Beatles' longtime sound engineer, wrote in his memoir Here, There, and Everywhere that it was Paul McCartney reacting to a botched note. Emerick claims that John Lennon insisted they leave the swear buried in the final mix. "Paul hit a clunker on the piano and said a naughty word," Lennon said. "Most people won't ever spot it ... but we'll know it's there."