On a quiet street lined with 18th-century Georgian houses behind Westminster Abbey, Garry Usher winds the mechanical clock on the gas street lamp and gives the glass globe a polish.
He steps down off his ladder and looks up with satisfaction as the soft, warm light lifts the dark winter evening, and moves on down the street.
Despite nationwide budget cuts that have reduced local services and seen street lights dimmed to save money, 1,500 gas lamps in London are still maintained by hand.
They are the last of tens of thousands of lamps that were first introduced in the capital 200 years ago, a marvel of modern technology that brought life to the once dark and dangerous streets.
While many London residents are oblivious to their presence, the lamps are protected by local authorities as a piece of history -- and new ones are even being installed.
"They're lovely. It's a fantastic form of lighting, not as harsh as electric," Usher told AFP as he went on his rounds.
The 50-year-old, an engineer with the British Gas energy firm, used to maintain central heating but began working on the lamps because it gave him Saturdays off to play rugby.
Now he leads a team involving four other "lamplighters" who maintain the lamps, half of which still have mechanical clocks that need re-winding every 14 days.
The others run on electrical timers which need their batteries changed every six months, while the various parts also need checking regularly.
"You're touching history everywhere you go -- it's a privileged job," Usher said.
- Burning sewer smells -
Gas lamps became common across Europe in the mid-19th century. Before that, walking the streets at night was a dangerous business.
In London, you could pay a "link boy" a farthing to guide your way with a candle, but there was always a risk he might rob you blind.
Initial reaction to the first demonstration of gas lights in 1807 -- the first on any street in the world -- was mixed, not least because the early gas lines could be dangerous and there was the odd explosion.
But when King George IV ordered their widespread introduction in 1814, they quickly caught on.
Some lamps had a dual purpose of lighting the streets and clearing the smells from London's underground sewers.
The Webb Sewer lamp drew up gases from the sewers down below and burnt it off. One such functioning lamp still exists, next to the Savoy Hotel near the River Thames.
- Back in vogue -
As late as the 1970s, many gas lamps in London were still lit by hand each evening and extinguished every morning.
Now they all have a permanent pilot light burning and the mains gas flows on a timer, heating up the "mantles" -- small ceramic meshes resembling bulbs, that become white hot and give off a glowing light.
They lend a magical quality to the streets and in St James' Park, near Buckingham Palace, are the only source of light, offering a rare glimpse into what it might have looked like in Dickensian times.
The lamps survived the arrival of electricity and the Blitz bombings in World War II, and these days the biggest threat is the traffic.
Originally designed to stand above a horse and cart, many have been extended upwards to stay out of the way of trucks, although some still get hit and must be repaired.
They are not just about history, however.
A number of new gas lamps have been installed in recent years, including one requested by the architect behind the new Apple store in Covent Garden.
"There's no chance of these lamps disappearing," said Iain Bell, operations manager at British Gas.
"If anything we're getting more calls to install them."