The conmen gained the trust of the elderly couple by offering condolences for their daughter and son-in-law. They had photograpahs in the room of both of them.
There were also photos of Harold's mum receiving a telegram from the Queen on her 100th birthday and a picture of the ship he served on during the Second World War - a mine sweeper that took part on D-Day.
The conmen then started doing a bit of work on the wall and said there was a problem with a bush near the house; the roots were affecting the foundations and urgently needed to be removed. They then insisted on being paid £3000 in cash.
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The eagle-eyed resident spotted the mistake on signs just feet apart in south London.
The victim was attacked after bumping into a man at the ticket barrier at Putney Station.
The victim, who is his 40s, was found near the edge of palace grounds.