A protest letter written by John Lennon to Queen Elizabeth II was recently discovered inside the sleeve of a used record in a man's attic.

The anonymous owner purchased the album for around US$12, but the letter from Lennon is estimated to be valued at around US$73,000.

Lennon penned the letter to explain to the Queen why he was returning his Member of the British Empire medal. He and the rest of the Beatles received the award in 1965.

In the letter, Lennon wrote, "Your Majesty, I am returning this MBE in protest against Britain's involvement in the Nigeria-Biafra thing, against our support of America in Vietnam and against Cold Turkey slipping down the charts."

Lennon signed the letter "John Lennon of Bag," so it was likely written during his "bagism" campaign with his wife Yoko Ono.