Like most visitors to London, Klaus Matzka and his teenage son Loris took several photographs of some of the city's sights, including the famous red double-decker buses. More unusually perhaps, they also took pictures of the Vauxhall bus station, which Matzka regards as "modern sculpture".
But the tourists have said they had to return home to Vienna without their holiday pictures after two policemen forced them to delete the photographs from their cameras in the name of preventing terrorism.
Matkza, a 69-year-old retired television cameraman with a taste for modern architecture, was told that photographing anything to do with transport was "strictly forbidden". The policemen also recorded the pair's details, including passport numbers and hotel addresses.
In a letter in today's Guardian, Matzka wrote: "I understand the need for some sensitivity in an era of terrorism, but isn't it naive to think terrorism can be prevented by terrorising tourists?"
The Metropolitan police said it was investigating the allegations.
In a telephone interview from his home in Vienna, Matka said: "I've never had these experiences anywhere, never in the world, not even in Communist countries."
He described his horror as he and his 15-year-old son were forced to delete all transport-related pictures on their cameras, including images of Vauxhall underground station.
"Google Street View is allowed to show any details of our cities on the world wide web," he said. "But a father and his son are not allowed to take pictures of famous London landmarks."
He said he would not return to London again after the incident, which took place last week in central Walthamstow, in north-east London. He said he and his son liked to travel to the unfashionable suburbs.
"We typically crisscross cities from the end of railway terminals, we like to go to places not visited by other tourists. You get to know a city by going to places like this, not central squares. Buckingham Palace is also necessary, but you need to go elsewhere to get to know the city," he said.
He said the "nasty incident" had "killed interest in any further trips to the city".
Jenny Jones, a member of the Metropolitan Police Authority and a Green party member of the London assembly, said she would raise the incident with the Met chief, Sir Paul Stephenson, as part of discussions on the policing of the G20 protests.
"This is another example of the police completely overreaching the anti-terrorism powers," she said. "They are using it in a totally inappropriate way.
"I will be raising it with the commissioner. I have already written to him about the police taking away cameras and stopping people taking photographs and made the point that if it was not for people taking photos, we would not know about the death of Ian Tomlinson or the woman who was hit by a police officer."
A spokeswoman for Metropolitan police said: "It is not the police's intention to prevent tourists from taking photographs and we are looking to the allegations made." The force said it had no knowledge of any ban on photographing public transport in the capital.
