Sir Paul McCartney admitted he sometimes forgets the lyrics to his biggest hits.

The 76-year-old musician - who has released 18 solo albums, seven with Wings and 12 studio records with The Beatles - has penned countless timeless hits over the years, and he revealed it can be tough remember all the words when he's playing live.

Speaking to '60 Minutes' on CBS about preparation for his upcoming 'Freshen Up' tour, he said: ''When I'm doing shows I listen to a lotta music, Beatles music, Wings music, to see what ones we're gonna do.

''And to learn them... There's too many. Too many words. Too many notes. They're very hard. I mean, you know, it's not like they're all three chords.''

The legendary musician - who released 'Egypt Station' last month - also revealed how competition drove his and John Lennon's songwriting as they made sure to keep up with each other.

He added: ''Not openly, but we - we later admitted, 'Yeah, you know, so Paul's written a good one there, I better get going.' And I would similarly, 'Hmm, that's a bit good, right, here we go, come on.'

''If he'd have written ['Strawberry Fields Forever'], I would write 'Penny Lane', you know, and it's - he's remembering his old area in Liverpool, so I'll remember mine.''

Meanwhile, Paul recently admitted he was ''put off'' performing The Beatles hit 'Helter Skelter' because of the song's association with the late cult leader Charles Manson, who named his prophecy of a race war between Caucasians and African-Americans after the track.

After listening to the LP repeatedly, Manson believed that the band had tapped into his spirit and had foreseen the same oncoming racial violence that he had and that he intended to spark with the actions of the Manson Family and their own music album.

In August 1969, the cult were responsible for the murder of Sharon Tate and four others at the Los Angeles home she shared with Roman Polanski in August 1969.

One of the killers wrote ''Healter (sic) Skelter'' in blood on the refrigerator of the house in which the murders took place and numerous references to other Beatles songs, in particular 'Piggies' from the 'White Album', were also scrawled in blood at the scene.

The singer previously said: ''I thought, I'm not doing ['Helter Skelter'], you know, because it was too close to that event, and immediately it would have seemed like I was, either I didn't care about all the carnage that had gone on or whatever, so I kept away from it for a long time.''