WHEN curators at the archeological museum in Madrid got their hands on what seemed to be a fine piece of Islamic art last year they did not want to let it go. They were entranced by the bronze aquamanile, or water carrier, in the shape of a dove.

Aquamaniles are rare and extremely valuable. One in the shape of an eagle in the Hermitage, St Petersburg, is regarded as priceless. The Madrid dove was almost unique, because the original Arabic inscriptions had been overlaid in Latin — the embodiment of the reconquest of Spain by Christians in the 15th century after centuries of Moorish rule.

The museum, which has the role of safeguarding evidence of Spain’s heritage, refused a request from Sotheby’s, the auction house, for an export licence. Instead it persuaded a Madrid bank to buy the dove for the equivalent of £900,000 and donate it to the nation in lieu of taxes. It is now on show in the museum.

Unfortunately, the dove is almost certainly a fake, according to friends of an English master forger. They believe he made it in a garden shed in Herefordshire out of old bath taps.

Nor was it unique. Many apparently valuable medieval bronze artefacts sold through top auction houses and dealers over the past decade may have been the work of the same man.

An investigation has been launched into the activities of William “Bill” Foster, who allegedly fooled the art establishment by selling forged ancient artefacts knocked up in the back garden of his home in Wigmore, Herefordshire.

There is evidence that Foster, who died in April, made £1m-plus by selling his fake artefacts to dealers and auction houses for more than a decade.

This weekend, Sotheby’s said it had launched an investigation. The ministry of culture in Spain is also re-examining the authenticity of the dove.

The story of how Foster allegedly tricked the art world has emerged since the father of six died from cancer. Friends, who do not wish to be named, say they are telling his story because he had always intended to cause embarrassment by publicising his forgeries.

“He wasn’t interested in the money,” one said. “He lived in a tiny bungalow, drove a second-hand car and smoked like a trooper. It was a game to him.”

Foster told his friends he had served in the Household Cavalry and the former Rhodesian police force. A gifted craftsman, he made musical instruments. Then he bought a small forge and began to produce dozens of candlesticks and figurines in his garden shed by the “lost wax” method used by medieval artisans.

Neighbours report seeing him with books on Islamic and medieval art and say he bought bags of Victorian brass taps from local salvage dealers. Out of them he was able to produce metal alloys similar to those found in artefacts up to 1,000 years old.

“Bill would go to great lengths to purchase the metal analysis reports on medieval pieces so he could produce accurate copies,” one friend said.

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