The type-written 1971 letter, which proves the two Beatles weren't always best friends, is available at an upcoming RR Auction in Boston, Massachusetts.

In it, Lennon bashes MCCartney and his then-wife Linda for their criticism of his decision not to announce he was leaving the Beatles the year before (70).

"About not telling anyone that I left the Beatles - PAUL and (Beatles manager Allen) Klein both spent the day persuading me it was better not to say anything - asking me not to say anything because it would 'hurt the Beatles'... remember?" he wrote.

Taking aim at Paul directly, John added: "I was reading your letter and wondering what middle aged cranky Beatle fan wrote it," Lennon wrote, while also poking fun at his former bandmate's thoughts about their band's legacy.

"Do you really think most of today’s art came about because of the Beatles?" Lennon added. "I don’t believe you’re that insane - Paul - do you believe that?

"When you stop believing it you might wake up! Didn’t we always say we were part of the movement - not all of it? - Of course, we changed the world - but try and follow it through - GET OFF YOUR GOLD DISC AND FLY!"

The Lennon/MCCartney letter is up for auction until 17 November (16), and is expected to sell for more than $20,000 (£16,000).