Paul Wyman was volunteering in the Brentwood's Oxfam branch when he noticed in a package of donated goods, an odd-looking banknote of £100 Palestine pounds issued in 1920, Britain's The Daily Mail reported.
Wyman, who located the note, chose not to put it on the shelves and instead called an auction company, who appraised it at £30,000.
But when it went under the hammer at Spink auction house in London, it sold for a whopping £140,000, the newspaper said.
Wyman said: “I realized that I was holding something in my hands that was incredibly rare. I couldn’t believe it when it went for £140,000.”
The note was given to the store by a mystery donor in October 2020, and it was evaluated at an auction house in February 2022.
"The auctioneers originally valued it at £30,000 and I was amazed at that already - never mind £140,000,” Wyman added.
Bidders worldwide, including the United States and the Middle East, submitted offers in the hope of securing the note.
The money the note was sold for will go towards Oxfam's charitable work.
Wyman said: "It’s brilliant to know I played a part in raising so much money for Oxfam’s work helping the world’s poorest people."
Elaine Fung, a banknote specialist for Spink, said: "Less than ten of these banknotes are known to exist. It would have been issued to a high ranking official at the time as a token of appreciation for their services.”
Lorna Fallon, retail director for Oxfam, said: “We are so grateful to Paul and the Brentwood shop team for spotting this banknote, not to mention the generous member of the public who donated it to us.
She added, “We are delighted that the banknote has raised so much money for Oxfam’s work around the world, which includes helping people in East Africa who are at risk of famine, and assisting refugees from Ukraine.”
The auctioned banknote was £100 Palestine pounds, which was the currency at the time, and it was given to high-ranking officials during the British Mandate in Palestine in 1927.