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The problem came to light after an auctioneer, alerted by a dealer at a viewing, checked with other rooms to see if they had had similar difficulties. At least one other auction house confirmed that the same vendor had tried to pass off suspect material through them. Several pieces had realised substantial sums comparable with those of period pieces.

Contacting both Scotland Yard and ATG, the auctioneer told us: “They tend to send in six to eight lots of flatware by post, giving sensible reserves. At first glance it all looks genuine 18th and 19th century material but, on closer inspection, you can see that the pieces have been chemically altered and are the wrong colour.”

Collectors’ spoons

All the suspect items detected so far have been spoons – small collector’s pieces including trefid, caddy and double-ended medicine spoons. They are usually in very good condition with crisp, clear hallmarks. However, some of the hallmarks have been struck back to front or are in the wrong place. On some pieces where one would expect to find just a maker’s mark, full marks appear. They are thought to have been made in China.

The four auctioneers who are known to have discovered that suspect material has passed through their rooms have called back the lots. They are strongly recommending that anyone else who fears the same may have happened to them should submit suspect items to the Antique Plate Committee at Goldsmiths’ Hall for testing. However, for that to happen they would need the cooperation of the vendor.

Anyone who believes they may have come across similar items is asked to report them to the Antique Plate Committee on 020 7606 8971, Scotland Yard’s Art and Antiques Squad on 020 7230 2150, or ATG on 020 7420 6686.

• Six respected dealers in English watercolours have written to ATG to draw attention to “the spate of very recent forgeries of Rowlandson watercolours” appearing at regional auctions in recent months.

The works, on old paper, appear to be direct copies of authentic pictures and have typically been catalogued as “attributed to” or “circle of”, which would suggest to the unwary that the offered works were at least of the correct period, if not actually by Rowlandson.

According to Clifford Street, London dealer Lowell Libson the works are clearly very recent. For example, two suspect watercolours that appeared recently in a Surrey auction were copies of genuine Rowlandson’s sold by Sotheby’s in London just a few months earlier.

The letter, signed by Lowell Libson, Andrew Wyld, Gabriel Naughton, Bill Thomson, Martyn Gregory and Andrew Edmunds, appears in Letters to the Editor on page 55 of the Antiques Trade Gazette 1699.