A pair of Mahatma Gandhi's glasses will go on sale after staff at the East Bristol Auctions, the largest auction house in South West England, found them in a plain envelope.

Auctioneer Andrew Stowe said: "Someone popped them into our letterbox on a Friday night and they stayed there until today – literally hanging out.

"One of my staff handed them to me and said there was a note saying they were Gandhi's glasses. I thought 'That's an interesting one' and carried on with my day."

Upon investigating, Stowe said he almost "fell off his chair" to discover the circular rimmed, gold-plated glasses, had been worn by the Indian civil rights leader.

"I phoned the guy back and I think he nearly had a heart attack," said Stowe.

The glasses are expected to raise more than $19,600 and were the most valuable things in the company's history.

Stowe said the owner "nearly had a heart attack" when he was told their value.

Stowe said the owner told him the glasses had been handed down from generation to generation in the owner's family, after a relative met Gandhi on a visit to South Africa in the 1920s.

"We looked into the dates and it all matches up, even the date Gandhi started wearing glasses. They are probably one of the first pairs of glasses he wore as they are quite a weak prescription," he added.

Stowe said there had been a lot of interest in the glasses, especially from India, but that it was fortunate they reached him intact.

"They were just in a plain white envelope. They could quite easily have been stolen or fallen out or just ended up in the bin. This is probably the most important find we have ever had as a company."

The glasses are going to be sold as part of an online-only auction on August 21..