The two-hundred -year-old false teeth of a wealthy archbishop with a host of mistresses have been discovered on the site of London's new Channel Tunnel station at St Pancras.

The extraordinary set of dentures, labelled "priceless" by experts, has gone on show at the Museum of London on Friday.

Even though the yellowy teeth are set in a bed of sickly purple "gums", two centuries ago the set would have cost as much as £105 - the price of a coach, annual fees for two children at the poshest of schools, or more than a year's wages for a housemaid.

Made of porcelain - a revolution in dental prosthetics at the time - the teeth were found fitting snugly in the skull of Arthur Richard Dillon, the archbishop of Narbonne.

'Colourful character'

Dillon was the highest ranking of around 8,000 clergy who escaped the guillotine during the French Revolution by fleeing the country.

"He was a very colourful and controversial character," said Phil Emery, the archaeologist who led the excavation. Although he was supposed to remain celibate as a Catholic clergyman, Dillon had "lots of mistresses".

The French king Louis XVI knew him well, and once asked him how he managed to spend so much money. According to research by Museum of London specialist Natasha Powers, Dillon had several large properties and kept a pack of staghounds for hunting. Yet despite his annual diocese income of 250,000 livres, the archbishop gambled most of his fortune away in Paris - leaving unpaid debts of 1.8 million livres.

His expensive false teeth were a sign of his status, Powers wrote in the latest edition of the British Dental Journal. They were "teeth for preaching, for public appearance." Nevertheless, "they were often difficult to eat with". At the dinner table people usually removed them with pride - a habit mocked by 18th century cartoonists.

Urine as tooth cleaner

At the time of Dillon's death in 1805, a diet of refined sugar and carbohydrates caused widespread bad teeth. In one sample - people buried at Spitalfields crypt in east London, nine out of ten had tooth decay.

Fans and perfumes were used to disguise the smell of rotting teeth. "Teeth" was even named as a cause of death in the Bills of Mortality of London, possibly referring to septicaemia from rotten teeth and rotting ivory dentures.

Surprisingly, toothpastes and -powders were widely available - although brushes were used only by the rich. One French dentist, Pierre Fauchard, even recommended using your own urine as a tooth cleaner.

Earlier false teeth were made of hippopotamus ivory, bone and even reclaimed human teeth set in gold. "Waterloo teeth" referred to teeth removed from the dead on the battlefield of Waterloo in 1815.

Experts believe Dillon's porcelain teeth may have been made by the Parisian dentist Nicholas Dubois De Chemant. He patented the method to make individual dental moulds of bees wax or plaster, and then casting perfectly fitted porcelain dentures.

Like Dillon, De Chemant also fled Paris and came to London, where he had a contract with Wedgwood to supply his porcelain.

'Extremely rare'

The archbishop died at age 85 as part of the vibrant French emigre community in Somers Town - now better known as Euston and King's Cross just north of central London.

Two centuries later, 1,500 bodies - including several French emigre - had to be exhumed from St Pancras burial ground to clear the land for the new Channel Tunnel Rail Link platforms. Archaeologists of the firms Gifford and Pre-Construct took a year to complete the mammoth task in 2002 and 2003.

Dillon was found in a lavishly engraved coffin, lined with lead to preserve his remains. His false teeth were almost completely intact - only missing some of its glaze and one of the two gold springs that held the set together.

The "extremely rare" set of teeth was "a unique archaeological find", Emery said. "They illustrate that the technology for dental prosthetics was extremely advanced at the time."

All the remains - bar the teeth - have since been reburied at East Finchley cemetery in north London.

And the dentures? They are now grinning at the public from a display cabinet near the entry hall of the Museum of London.