With their distinctive design and reassuring engine rumble, London's black cabs stand out - like fish and chips and Big Ben - among Britain's most cherished icons.
London's black-cab drivers believe they are the best in the world. And given their years of gruelling study to earn the right to get behind the wheel in the British capital, it may well be true.
Black-cab drivers, many of whom earn a comfortable living, have all passed The Knowledge, the legendary test of geographical knowledge that dates back to the 19th century.
But as GPS technology and the online ride-hailing app Uber threaten taxi businesses in cities across the globe, perhaps nowhere is the confrontation as resonant as in London.
Demand for The Knowledge has dipped since Uber opened its doors in London in 2012. According to official figures, between 2012 and 2014, the number of students signing up to study The Knowledge fell by more than a third.
"It's in serious danger of becoming a novelty vehicle," said Malcolm Linskey, 70, who for over three decades has run The Knowledge Point, one of London's largest training schools for black-cab drivers. He said demand for his beginner courses had halved since Uber came to town.
"The market share is dropping because less people are doing The Knowledge. I don't want to say it, but it's Uber. Why bother to do 3.5 years [of training] when you can do three weeks?"
The Knowledge requires students to memorise a mind-boggling 25,000 streets and 20,000-plus landmarks, including hotels, hospitals, theatres, museums, stadiums, housing estates, schools, universities, parks, pubs, police stations, prisons and places of worship. It takes, on average, three years to complete - about the same time as a law degree.
The city's private-hire drivers, a category that includes Uber, aren't required to pass The Knowledge. They rely instead on smartphones to help them ferry passengers across the British capital. It takes about three months to become licensed as a private-hire driver.
Unlike many other major cities, London does not limit the number of cabs. While London's population has grown in recent years, the number of black-cab drivers has remained stable at around 25,000. By contrast, the number of private-hire drivers over the last three years has risen by more than a third to top 92,000.
Steve McNamara, general secretary of the Licensed Taxi Drivers Association, said Uber had exacerbated congestion and air pollution and hit traditional cabbies' earnings by about 10 per cent during the day and up to 25 per cent at night.
"We are as much part of this community as red buses and we are being threatened," McNamara said. "We don't want cowboys running around clogging up our streets."
Uber has expanded quickly since launching in Britain, and today it has 20,000 drivers in London alone.
Its supporters say it has ushered in choice and convenience and is usually much cheaper. A recent trip in a black cab from Waterloo station to Heathrow airport cost $149. The same trip with a driver for Uber cost $100.
Not that it's been an easy ride for Uber. Traditional taxi drivers throughout Europe have railed against the California company, arguing it circumvents the rules adhered to by conventional taxis.
Its services have been barred or scaled back in countries from Spain to Belgium to France.
But change is in the air. The European Court of Justice is reviewing a case that could have widespread implications as it is expected to consider whether Uber is a digital service company or a transport company.
In London, a crackdown against Uber and other ride-hailing apps could be looming with new proposals that could tip the advantage back to black-cab drivers. (In New Zealand there are proposals in the mix to place more regulation on Uber drivers as part of a government review of the taxi industry.)
Transport for London (TfL), the city's transportation authority, has proposed new private-hire regulations that could address some of the criticisms of the black-cab industry. It claims Uber is operating in a similar fashion to traditional black cabbies while bypassing their regulations, like learning The Knowledge or meeting strict vehicle specifications.
The proposals include a five-minute delay after booking a car and a ban on showing cars immediately available in the area - a feature much loved by Uber customers. They would also require drivers to pass map reading and English language tests.
The changes "would mean an end to the Uber you know and love," Uber said in response. More than 200,000 people signed a petition opposing the changes. A decision will be made in this year.
Jo Bertram, Uber's regional general manager for Britain, Ireland and Nordic countries, argued in favour of lightening the load on black cabs rather than increasing regulations for Uber.
"These plans seem to be trying to level the playing field between taxi and private hire by imposing additional burdens on private hire that result in the negative outcomes for both consumers and drivers, rather than looking at how can we make some of the regulations on black taxis less onerous, which is something we definitely support," she said.
Some, including Conservative Party members of London's City Hall, have suggested that black cabbies and private hire would be on more equal footing if The Knowledge was significantly scaled back. It's an idea many black cabbies bristle at. They say that satellite navigation software doesn't always update fast enough and that under-trained drivers are easily flummoxed by traffic jams and road closures.
"Yes, it's an arduous process," said Danny Smith, a 30-year-old who has been training full-time for more than two years to become a London cabbie, zipping up and down the capital's narrow streets on his moped. On a recent day he was at a Knowledge school, going over "runs" with other students, known as "Knowledge boys and girls," who were marking off the names of streets he was calling out on giant laminated maps.
He said he hoped that becoming a black-cab driver would mean a lifetime of work and a decent salary, something he didn't think Uber offered its drivers, who held a small protest in London last month over falling pay.
Plus, for Smith there is a certain prestige. "To drive a London taxi is quite renowned," he said.
While London's population has grown the number of black-cab drivers has remained at around 25,000. By contrast, the number of private-hire drivers has risen by more than a third over the past three years to more than 92,000.
The Knowledge requires students to memorise 25,000 streets and more than 20,000 landmarks, including hotels, hospitals, theatres, museums, stadiums, housing estates, schools, universities, parks, pubs, police stations, prisons and places of worship.