What would you do if you found a wallet in the street? Would you return it? Would the cash still be there when it made its way back to its owners? Depressingly, most of us would keep the wallet, and pocket the cash. However, there are some Good Samaritans who buck the trend - and over the years have returned some truly astonishing sums of money.
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Reader's Digest carried out a famous study a few years ago, dropping 12 wallets containing £30 and contact details in 16 cities around the world - and ranking the honesty of their inhabitants. London was included in the study, and only five of the 12 were returned. It put the city ninth out of 16 for honesty -which is pretty depressing.
We can take some comfort from the fact that it could be worse: in Portugal only one of the wallets was returned - and in that case it was by a Dutch couple who were on holiday there at the time.
However, there is more comfort to be found in the exceptions to the rule. In some cases, Good Samaritans have returned some incredible sums - and made a life-changing difference to the person who had accidentally mislaid the cash.
1. In 2014, Zhao Lei, a taxi driver in Harbin, in the north-eastern province of Heilongjiang, dropped a couple off at a car dealership, and drove off with £16,000 in a bag on the backseat - which they had intended to buy a car with. He handed in the money at work, and they tracked the couple down. They offered him £1,000 as a reward, and despite the fact it was two-month's wages, he told them he didn't want to profit from their misfortune.
2. In 2013, Glen James, a homeless man in Boston, flagged down a police car. He handed over a backpack containing $2,400 in cash and $40,000 in traveller's cheques, which he had found at the shopping mall. The money was returned to its owner, and the press picked up the story. A man from Virginia read the story, and set up a crowdfunding page for him - in two days it raised $110,000.
3.Later that year, a homeless man in Atlanta found a woman's wallet in a rubbish bin. He could see from the contents that she was a tourist, so he went to several hotels to see if he could track her down. When he eventually found her, the hotel staff rewarded him with an overnight stay, new clothes and $500.
4. Back in 2011, a man in Utah found $45,000 hidden around his new home. He discovered that the former owner was a father of six who had a habit of hiding money, so returned the cash to his children.
5.In the same year, 75-year old Billie Watts found a bag containing $97,000 in the toilets of a Cracker Barrel restaurant in Tennessee - along with two photographs. She took the money home, but called the restaurant, and said that anyone who had left something in the toilets should call her. A quarter of an hour she had a call from the rightful owner of the bag - who thought she had lost every penny she made in the sale of her house.