Post Office Mauritius
In 1902 a French schoolboy collector rummaged through the old correspondence of a Bordeaux wine merchant. The boy knew that the firm did business with Mauritius, and he thought there might be an outside chance of finding a very rare stamp - the legendary Post Office Mauritius (illustrated above on the envelope). It's called the "Post Office" because it mistakenly bears these two words instead of "Post Paid". Two denomindations were produced: a Penny Red and a Twopenny Blue, and there were only ever 500 of each. The boy unearthed two letters with the stamps - one, incredibly, had both denominations. He sold them to a dealer the following year for the then very tidy sum of pound;2,800. A similar cover sold in 1993 for pound;3 million. In 1904, the Duke of York, later George V, bought a Post Office Mauritius for the royal collection, which is now a priceless national treasure.
The most famous stamp outside the collecting world is the Penny Black. The fame is well deserved, because it's Rowland Hill's Penny Post stamp - the one that started it all. It shows Queen Victoria, but not the name of the country. Why should it? Britain was the first country to have stamps - and ever since, it's the only country allowed this dispensation.
Contrary to popular perception, the Penny Black is not rare. It's value lies in its fame and its history. Authorities differ about how many were printed, but it's in the millions. If you want one for your school collection - and why not illustrate your history lessons with the real thing? - expect to pay about pound;10 from a dealer. But just to illustrate the effect of condition - a really fine one, with no creases, good margins and perforations, will set you back more than pound;200. And if you find a whole sheet of 240, in magnificent condition, you may be about to be able to buy that place in Tuscany.
The trouble with the Penny Black was the postmark. A black cancellation was difficult to see, and the Post Office had endless trouble finding a coloured alternative that wasn't easily wiped off. Hill's answer was to change the colour of the stamp to red.
You can buy a Penny Red for, well, pennies but some are worth up to pound;10,000. To see why, you need a magnifying glass. If you look into the pattern on the edge of the stamp you'll see a tiny number 77. That says it was printed from plate 77 and only nine exist.
British Guiana 1 cent Magenta
You couldn't get a stamp rarer than this, because there's only one left in existence. In 1856, a shipment of stamps was due in British Guiana from Britain. It didn't arrive in time and so a small batch was made locally.
They weren't very well printed (it's not a very attractive stamp) and were authenticated by the initials of postal officials. In 1873 a British Guiana schoolboy found one on a letter in his house and put it in his album. He soon sold it for six shillings, because he wanted to buy some more colourful stamps, and from then on, as it was gradually realised that no others seemed to have survived, it exchanged hands for ever-increasing amounts - $75,000 in1940, 10 times that in 1970. Finally, in 1980 it was sold to its present owner John du Pont of Pennsylvania (who is, incidentally, doing 30 years for murder) for $935,000.
In the 1980s, the stamp world was intrigued by the apparent appearance of a second of these stamps, allegedly owned by a Romanian dancer who'd inherited it from her grandfather. Investigation has since proved it is a forgery.
British pound;1 Postal Union Commemorative of 1929
The "pound;1 PUC" isn't among the most fabulously valuable of stamps, but with its superb George and Dragon design, many collectors believe it's the most attractive British stamp ever. You can have one in mint condition for, at most, pound;750.
Upside down aeroplane
Some stamps are rare because they show errors. In 1918 W J Robey of Washington DC, bought a sheet of 24 cent airmail stamps and noticed the upside down aeroplane. No sooner had he got them home than postal inspectors arrived and threatened him with dire consequences if he didn't give them back. He kept his nerve, showed them the door and within a week had refused first $500, then $10,000. Eventually he made $15,000 for what turned out to be the only known sheet. The sheet was broken up and each stamp now makes up to $20,000.
1851 Hawaii 2 cent Missionary
It's called the "Missionary" because they were used by missionaries writing home to the US. They were fragile stamps, and only 15 of the 2 cent denomination survive. One belonged to Gaston Leroux of Paris, who in 1891 was found murdered. There was no apparent motive, until a detective who was a stamp collector came on the scene. He found this rare stamp missing and then, through dealers, tracked down Hector Giroux who, sure enough, had the stamp in his collection. An example in good, unused condition would probably fetch at least pound;750,000.
Cape of Good Hope Triangular
The Cape of Good Hope was seized by Britain from the Dutch in 1806, and granted limited self-government in 1853, as the Cape Colony. Its stamps were not only the first of triangular shape but the first to come from Africa.
The early 1cent and 4 cent stamps are quite rare - an excellent 4 cent stamp may cost pound;2,000, but you can pick one up for pound;200.
Old, high-value Great Britain stamps look good, and are sometimes valuable.
The pound;5 Orange from 1867 is worth pound;6,000 in fine condition.