Sir Paul McCartney and John Lennon wrote EIGHT DAYS A WEEK just so Lennon could buy himself a swimming pool with the profits.

McCartney knew the Beatles were rich when he and his songwriting partner found themselves working on a tune with the sole intention of landing Lennon a pool for his Esher, England home.

Speaking exclusively to British rock magazine Mojo, he recalls, "Around the HELP! time he'd be getting an extension on his house or something, and the joke used to be, 'OK! Today, let's write a swimming pool.' It was great motivation.

"You've got to be able to take it lightly. But then, in the next three hours, Help! appears from nowhere, you'd suddenly get the idea this'll be a hit, this is a good one. You became aware what you were doing was making money. Making good money.

"Obviously, these were the jokes we made to keep ourselves sane and comfortable. We were actually writing what we considered to be art... We weren't just writing s**t for a swimming pool."