Countdown host Nick Hewer has had his £10,000 watch stolen after agreeing to take a photograph for two thieves posing as tourists.
The International Watch Company (IWC) watch was snatched from his wrist, he told his 190,000 followers on Twitter.
"NEVER agree to take photo of stranger with their camera phone," he says. "They'll steal your watch so fast when you hand phone back. Anyone seen my IWC?"
Theft on the wane?
Figures released by the Office for National Statistics last month show that theft from the person has fallen by 10% in the last year. It accounts for 3% of all crime. But there's wide variation in the risk, with cities far more dangerous than rural areas: 43% of cases occurring in London's Metropolitan Police Force area alone.
Most victims are male and most thieves female, according to the Met, and busy public places are the most dangerous spots. Phones are the most commonly-stolen items.
"Street robbery often occurs in and around transport hubs, where commuters, often lone women are targeted," says Metropolitan Police Service commander Simon Pountain.
"Many robberies happen when people check their phones just after leaving underground stations, or when they are going about their business and may be distracted. Adults who have consumed alcohol and have less awareness of their surroundings are also more vulnerable."
Travel company Justtheflight.co.uk recently warned of the commonest street theft techniques around the world. In London, apparently, using distraction is the technique of choice.
"A man will perform a game such as guessing which cup a ball is in, or a magic trick, on the side of the street, and will have a group of accomplices disguised as tourists watching his show," it says.
"This is to make you curious and want to go over and watch him. While you're distracted and concentrating on the performer, his accomplices will pickpocket you."
Other scams include the offer of a friendship bracelet or the spilling of something on your jacket - helping you wipe it off gives the thief a chance to pick your pockets.
"Some scams are quite obvious once they have occurred, with the victim realising they have been cheated but only after it is too late," says the company.
Read more on scams:
Fake nun and priest scam hits Italian elderly
Summer scamwatch: holiday club fraud
The pickpockets' tricks, and how to beat them