Hundreds of wallets were planted on the streets of Edinburgh by psychologists last year.

nearly half of the 240 wallets were posted back

Richard Wiseman, a psychologist, and his team inserted one of four photographs behind a clear plastic window inside, showing either a smiling baby, a cute puppy, a happy family or a contented elderly couple. Some wallets had no image and some had charity papers inside.

When faced with the photograph of the baby people were far more likely to send the wallet back, the study found. In fact, only one in ten were hard-hearted enough not to do so. With no picture to tug at the emotions, just one in seven were sent back.

The baby photograph wallets had the highest return rate, with 88 per cent of the 40 being sent back. Next came the puppy, the family and the elderly couple, with 53 per cent, 48 and 28 respectively. At 20 per cent and 15, the charity card and control wallets had the lowest return rates.