The art of forgery is as old as the art trade itself. From an ancient letter purportedly written by Jesus Christ to a friend that first turned up for sale in 300AD to a contemporary piece of pottery by the Turner Prize-winning Grayson Perry, imitations pervade the markets.

They are everywhere from e-Bay to the most reputable auction house. Even some of our most famous pictures — take the National Gallery’s sumptuous Samson and Delilah by Rubens, for example — are constantly under question. As much as 40 per cent of what turns up for sale may be composed of some type of fake, Thomas Hoving, an art historian and former director of New York’s Metropolitan Museum, once suggested.

The search for authenticity starts to feel a bit like some modern equivalent of the quest for the Holy Grail.

New technologies have not helped. Where once a crook would have had to plaster the back of a canvas with scraps of Victorian newspapers and old auction house stickers, now the up-to-date computer-literate trickster can fake pretty much anything down to the documentation — false catalogue entry included — that dealers depend upon to authenticate a work.

And, as collectors in a competitive market start to seek alternatives in ever more specialised areas, there are plenty to capitalise on scant knowledge, a paucity of published references and too much wishful thinking to produce lucrative imitations.

Still, perhaps Grayson Perry should remember Picasso, the most frequently copied of modern artists. He was asked what he did when confronted by a work that was purportedly by him. “If I like it, I say it’s mine. If I don’t, I say it’s a fake,” he said.

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