It cost only one old penny to send to King's Lynn.

But now, 173 years later, this exceptionally rare Victorian letter sheet is set to fetch between £10,000 and £12,000 at an auction – and all because someone stuck a postage stamp in the wrong corner.

The letter sheet was sent to King's Lynn from London on April 17, 1841, just two months after the introduction of the Penny Red postage stamp.

This had replaced the short-lived Penny Black, Britain's first adhesive postage stamp, which was introduced in May 1840.

The Penny Red stamp ought to feature a black Maltese Cross cancellation.

But because the stamp was stuck in the top left hand corner instead of the right hand corner it was not cancelled, and a postal clerk cancelled it later with a red Tombstone datestamp.

Dominic Savastano, a postage stamps expert at London auctioneers Spink, said: 'It is a big rarity. This is the first Penny Red with a red Tombstone cancellation I have seen in 43 years. It should have been cancelled with a black Maltese Cross datestamp.'

The stamp is to be auctioned at Spink on May 14.

The name of the King's Lynn recipient on the letter sheet is smudged and illegible and part of the letter sheet is missing, which has slashed thousands of pounds off its value.

If the letter sheet were complete the item would be worth nearer £20,000.

The Penny Red postage stamp replaced the Penny Black in February 1841 due to the difficulty of seeing a black cancellation mark on the Penny Black.

In 1841 the Penny Red stamp was not perforated, which meant that each stamp had to be laboriously cut by hand from a sheet.

The letter sheet in question probably made the 108-mile trip from London to King's Lynn by horse-drawn mail coach, because King's Lynn railway station did not open until 1846 and Norwich railway station was not opened until May 1844.

Do you have a King's Lynn story? Email chris.bishop@archant.co.uk