McCartney and Linda, who is attacked by Lennon

The letter is believed to have been written at Lennon's Berkshire mansion, Tittenhurst Park.

At the time, the relationship between the four members of the band was rumoured to have seriously broken down.

Their record company Apple was breaking up and they were all suing each other.

Lennon's letter also illustrates his bitterness over what he considered to be the others' unfair treatment of his wife Yoko Ono.

He has a go at McCartney's wife Linda, comparing her to a "middle-aged, cranky fan".

Affection

And he launches into an attack of what he considered to be McCartney's conceited attitude to the worldwide adoration inspired by The Beatles.

"Do you really think most of today's art came about because of the Beatles?" asks Lennon.

Yoko Ono: Lennon said she was treated unfairly

"I don't believe you're that insane. Didn't we always say we were part of the movement, not all of it? Get off your gold disc and fly."

The letter also confirms that the band split up several months before any official announcement was made in April 1970.

In the recent Beatles Anthology, written by the three remaining band members, Lennon is said to have been the first to leave.

In the letter, Lennon shows that he was angry that he was made to keep quiet about it.

Lennon did however try to finish the letter on an affectionate note, signing it: "In spite of it all, love to you both from us two."

It is not known whether the letter was sent. It is being sold by an anonymous vendor, who bought it at auction in America in the early 90s.