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In most cases the woman – who was black, about 5ft 8in tall, in her fifties, wearing a mink coat and speaking in an educated (possibly American) accent – sought to gain the confidence of a dealer by spending up to three or four hours in a shop discussing potential purchases. Having chosen pieces to buy, and arranged to have the goods forwarded, she then either wrote cheques in the name of Michelle Martin (in one case for £50,000) or promised to wire money from her bank account the next day.

Only when she had left the shop (or when no payment was received) did the dealers realise that a small, easily concealed item of stock – and in one case a credit card – had been taken. A cold painted Bergmann bronze camel and a 10 by 14in (25 x 35cm) painting signed Niemann, its frame discarded on the shop floor, were among items taken.

A woman fitting exactly the same description, but using the name Joanna Gates and a different address, then used a similar method of operation to target dealers in the Fulham Road. Gary Jones of Kensington police said they now had a number of incidents on file that they consider to be linked.

Any information should be given to Kensington police on 020 7376 1212, quoting crime reference number 5601127/04.