The Beatles were sex machines in their early days on the road – sleeping nightly with strippers and gobbling down drugs, a new biography of the Fab Four claims.

The legendary rockers were so casual about sex that John Lennon and Paul McCartney once watched in amusement as George Harrison lost his virginity to a buxom German dancer, the book says.

“In the late ’50s in England, it wasn’t that easy to get it. The girls would all wear brassieres and corsets, which seemed like reinforced steel,” Harrison confesses in “The Beatles Anthology.”

But things changed in the early ’60s when the boys, all in their teens, got noticed and were invited to play in Hamburg, Germany, where they shared a room.

“My first shag was in Hamburg – with Paul and John and [the group’s first drummer] Pete Best all watching,” Harrison says.

“We were in bunk beds. They couldn’t really see anything because I was under the covers, but after I’d finished, they all applauded and cheered. At least they kept quiet while I was doing it.”

In the authorized bio, serialized in London’s Sunday Telegraph, McCartney says Germany was “a case of sex shock.”

“Suddenly, you’d have a girlfriend who was a stripper. If you had hardly ever had sex in your life before, this was fairly formidable,” Paul says.

“In Liverpool, all the girls wore very rigid girdles; it was medieval. Here, in Hamburg, they were almost flashing it. It wasn’t your average sweet virgin that you were mixing with.”

McCartney remembers that he and his bandmates were always walking in on each other during sex.

“That was the intimacy we had … I’d walked in on John and seen a little bottom bobbing up and down with a girl underneath him. It was perfectly normal: You’d go, ‘Oh … sorry,’ and back out the room,” he says.

“It was very teen-age: ‘Are you using this room? I want to have a shag.’ And you’d pull a girl in there.

“That’s why I’ve always found very strange the theory that John was gay … Not one of us has an incident to relate of catching John with a boy,” Paul says.

Aside from sex, The Beatles also got into drugs in a big way.

“We found pills, uppers. That’s the only way we could continue playing for so long,” Ringo Starr says.

“You could buy them over the counter. We never thought we were doing anything wrong, but we’d get really wired and go on for days.”

Harrison says Lennon would go berserk when he was high.

“Paul had a chick in bed, and John came in and got a pair of scissors and cut all her clothes into pieces and then wrecked the wardrobe,” he recalls.