Penny Black: One of world's first postage stamps to fetch up to £6m at auction

An example of the world's first postage stamp - the Penny Black - bearing an image of Queen Victoria is set to fetch as much as £6m at auction.

Launched in 1840, the item is "the earliest securely dated example of the first postage stamp", according to auction house Sotheby's, and is to be sold in London on 7 December.

The stamp is attached to a document dated 10 April 1840, from the archive of British postal service reformer Robert Wallace, a Scottish politician.

The Penny Black was first issued in the UK after inventor Sir Rowland Hill proposed an adhesive stamp to indicate pre-payment of postage.

At the time, it was typical for the recipient to pay postage on delivery.

But the Penny Black allowed letters of up to half an ounce (14 grams) to be delivered at a flat rate of one penny, regardless of distance.

"This is the first ever stamp, the precursor to all stamps, and unequivocally the most important piece of philatelic history to exist," Henry House, head of Sotheby's Treasures Sale, said in a statement.

"Though there are many hugely important stamps in collections both public and private around the world, this is the stamp that started the postage system as we know it."

It is one of three Penny Black stamps understood to have survived from the very first sheet of printed stamps - with the other two now part of the collection at the British Postal Museum.

The stamp's original owner, Alan Holyoake, a businessman and philatelist, came into possession of the stamp around 10 years ago.

He said: "The fact that Wallace signed, dated and issued his note... gives support to the fact that this is the very first example of a postage stamp, which of course every country now uses."

Mr Holyoake undertook an extensive three-year research project to determine its authenticity and the stamp has certificates from The Royal Philatelic Society and The British Philatelic Association.

Sotheby's said it is the first of its kind to be offered at auction, giving it a price estimate of £4m to £6m ($5.5m to $8.25m).

Back in June, the British Guiana 1c Magenta (1856) £6.2m stamp, believed to be the most valuable man-made item, returned to the UK from New York after 150 years.