Harry Potter and the Philosopher's Stone first edition could make £50,000 at Derbyshire auction

The book, unearthed by Hansons books expert Jim Spencer, has an estimate of £20,000 to £30,000.

However, it could fetch as much as £50,000 when it goes under the hammer on October 13, thanks to its good condition and the fact it is one of only 500.

It had been sitting on a book shelf for around 21 years when the owner randomly decided to check it – but never in his wildest dreams did he expect it to be a first edition.

The retired British expat, who lives in Luxembourg, said: “A couple of months ago when JKR bounced into the main news I decided to re-read the Potter series.

"I knew there had been a few first editions sold recently and Hansons was featured on the BBC website so, just to be safe, I checked the criteria.

“I did not think mine would be valuable as it was certainly not purchased when first published.

"I was very surprised and shocked to see that it did in fact tick all the boxes, but still could not quite believe it until I checked with Jim Spencer.”

Jim added: “True first issues are seriously scarce, only 500 were printed, 300 of which were sent to schools and libraries and this is extra rare because it’s one of the remaining 200.

"And yet this is my fourth one in just over a year.

"It’s a cliched phrase, but they really are the holy grail for collectors.

“This new copy deserves to do really well because it’s in astonishingly good condition – I would love to see it make £50,000.”