London is famed for its historic sites, its double-decker buses and its West End shows, but the city now has a more dubious distinction: Britain's public health agency says it has become the tuberculosis capital of Western Europe.

In response, health officials are taking to the streets in an effort to stop the spread of the infectious lung disease. A high-tech white van equipped with an X-ray machine is driving around London offering free check-ups.

Similar vans were once common in Europe and the U.S. in the 1950s but most disappeared about two decades later when TB rates dropped. But in recent years, the disease has surged in the U.K.

Last year, London had about 3,500 TB cases - more than the Netherlands, Belgium, Greece and Norway combined. It also had more TB than some African countries, including Eritrea and Gambia.

Britain as a whole however still pales against India, China and South Africa, which all have hundreds of thousands of TB cases.

"We kind of took our eye off the ball and now TB has become a big problem again," said Dr. Alistair Story, who runs the mobile TB van for University College London Hospitals.

He said the vast majority of TB in the U.K. is among the homeless, drug users and prisoners because they live in cramped conditions that make them susceptible to infections. Despite the belief that TB is being imported into the U.K. by recent immigrants, Story said their rates of infection are low.

"It's certainly not the case that we could have closed the borders and avoided the problem," he said, pointing out that other European countries with high levels of immigration, including France and Germany, have not had similar spikes of TB.

Tuberculosis is a highly infectious bacterial disease often spread by coughing or sneezing that kills more than 1 million people worldwide every year. It most often attacks the lungs and is highly treatable. More than 95 percent of TB deaths occur in developing countries. Experts are increasingly concerned about the rise of drug-resistant strains of TB, which require more toxic drugs to treat.

According to a global TB report issued Wednesday by the World Health Organization, 3 million people worldwide with TB are currently going undiagnosed. Another 16,000 people with drug-resistant strains are failing to get treatment.

London's 460,000-pound ($743,300) TB van has an X-ray machine whose scans can be instantly read by a radiographer. On average, the van picks up about one new TB case per week and screens about 10,000 people a year. If an X-ray looks worrying, staffers call a hospital to arrange confirmatory tests. The entire process of getting an X-ray and its results takes about 90 seconds.

On a recent morning, a steady trickle of patients streamed into the van after getting a ticket for a free X-ray from a nearby homeless shelter. To convince homeless people to get tested, the van relies on former TB patients including Horace Reid, 58, who got tested in 2009 after running out of breath trying to catch a bus.

"I didn't know anything was wrong until I missed the bus and couldn't breathe," he said. "(The doctors) told me I had TB and that I could die."

Dr. Norman Edelman, senior medical adviser at the American Lung Foundation, said the van is a practical attempt to curb TB.

"The people most likely to get TB are the hardest to find, so it's good to go out looking for them," he said.

Danny Hastie, 20, got sick numerous times last year but didn't bother seeing a doctor. Recently in prison, he has been living on the streets for more than a year.

"I heard about this van and thought I would give it a go," he said. "It's (scary) at first because you're thinking, `Oh, I might have a chest infection,' but when they say that you're clear, it puts your mind at rest."

British experts said the van was a good way of finding TB cases among the homeless but said wider screening tests were needed.

Dr. Ajit Lalvani, chair of infectious diseases at Imperial College London, said 70 percent of people with latent TB who arrive in Britain are missed. They aren't currently infectious, but Lalvani said the TB bacteria could sicken them in the future and cause them to infect others. Catching these patients would require a more expensive blood or skin test that isn't commonly used.

"There is a vast reservoir of TB that comes into this country silently," he said. "The mobile van is providing a great service, but until we test more widely, we will never get rid of TB in the U.K."