(CNN) — For Londoners and visitors alike , they're an often overlooked quirk -- if they're even noticed at all. But the handful of green wooden sheds known as taxi cabmen's shelters have a fascinating history.

They date to 1875, back when horse-drawn Hansom cabs were the vehicle of choice for London's first taxi drivers.

A newspaper proprietor called George Armstrong started a fund, supported by the Earl of Shaftesbury, to make cabs more available and also ensure that drivers avoided taking breaks in "hostelries" -- the pubs of the day.

Hansom fellows

The cabmen's shelters have been part of the fabric of London since 1875. Barry Neild/CNN

The shelter was born and today they still serve cheap, hearty and very British food to London's "black cab" drivers.

In theory they're not open to the public, but there are some that sell drinks and snacks out of the back hatch -- just never inside, a space strictly reserved for cabbies.

Once there were 60 across the capital, but now there are only about a dozen left. Most are located in London's wealthiest areas such as Chelsea, Mayfair and the West End. Surprisingly, there isn't one in the whole area of The City of London, the financial heart of the capital.

Each shelter is compact in the extreme, taking up no more space than a horse and four wheeled cab would have measured in the 19th century. Some still feature the original tenders where horses would have been tethered and watered from a marble trough underneath.

Intimate interiors

Len (left) and Colin take up almost all the seating in the tiny cabin Chris Dwyer

Their tiny interiors can squeeze in a maximum of 10 drivers at once, meaning space is at an absolute premium.

Colin and Len have both been driving cabs for more than 40 years and, as Colin explains: "When you all sit inside a shelter it's very intimate. If you don't like the person you sit opposite, you might as well leave!"

Each shelter is run by one person, so if they happen to be sick or on vacation, then they don't open. All are Grade 2 listed monuments, a heritage designation that means they can't be touched. If refurbished, they have to be kept exactly as they are.

Some drivers have joked that the food served also dates from the 19th century, but generally classic British dishes are the order of the day. One of the most popular is a traditional British "roast dinner," of meat with potatoes, vegetables and gravy.

Home cooking at unbeatable prices

The traditional British roast dinner is the most popular item on the menu. Chris Dwyer

Len explains: "It's proper home-cooked meals at a reasonable price. For that and a dessert, two courses cost you between £5 and £8 ($6-$10) ."

Try finding those prices anywhere else in London.

In a shelter outside the Victoria and Albert Museum, one owner says there's a dish that's always in demand: chicken curry. Likewise in the city's Warwick Avenue district, flavors are hotter and distinctly more exotic in a cab shelter run by a Thai woman who apparently keeps her spice levels authentic.

Other menus written on whiteboards feature cottage pie, roast chicken and the iconic bangers and mash -- sausages with mashed potato.

In a vague nod towards healthy eating, salads are occasionally available -- but according to one regular, "I've never seen a driver order one."

The Kremlin

One of the shelters, known as the Kremlin, was renowned as a hotbed of revolutionary discontent. Barry Neild/CNN

London's cab drivers are renowned for their sense of humor and their often forthright opinions, often proffered whether passengers want to hear them or not.

"You could probably run the world from inside one of these cab shelters," Len explains. "We know how to fix things. We have a freedom to be opinionated about things and we can give an honest opinion, unlike politicians.

"One of the shelters used to be known as The Kremlin, because of all the left wingers who used to frequent it."

Most of all, London's black cab drivers are known for their extraordinary, encyclopedic command of the labyrinth of London, known as "The Knowledge." A notoriously tough exam to pass, it takes between two to four years to learn more than 25,000 streets, 20,000 landmarks and places of public interest -- and how to get between them as fast as possible -- with not a GPS equipped device in site.

Don't mention Uber

While salads have been on the menu, one regular says he's never seen anyone order one Chris Dwyer/CNN

Don't even mention the four letter word that cab drivers can barely bring themselves to say: Uber.

Such is the learning involved, it was even reported in research from University College London that completing The Knowledge permanently enlarges the hippocampus in cabbie's brains. But given changes in technology and demographics, it's proven increasingly difficult persuading young people to spend up to four years learning The Knowledge. A trend underlined by the fact that today there are more cab drivers over 70 than there are under 30.

One thing is clear in the cab shelters, namely that there's been no shortage of colourful characters gracing them over the years.

Most invariably had nicknames, including Maltese Frank, known for having just one tooth, Almost Human, seemingly not the most attractive of drivers, Wingnuts, Suffering Pete or Ashford 'Arry.

Death, taxes and army tea

Tea you could stand a spoon up in. Chris Dwyer

As he sips a strong cup of tea inside a shelter, Len is forthright about the value of his chosen profession.

"There are two certainties in life: death, and the fact that these are the best cabs in the world," he says. "They are the best vehicles, with the best drivers who know where they're going. Ninety nine point nine percent of them are nice guys who just want to earn a living and go the quickest way possible."

The taxi cabmen's shelters may have seen a decline since their heyday -- but the characters, opinions and many of the dishes served within them remain resolutely and defiantly old school.

Where to find the shelters

Chelsea Embankment , at north end of Albert Bridge

Embankment Place , close to Embankment Underground station

Grosvenor Gardens , near Victoria Station

Hanover Square , near Oxford Circus Underground station

Kensington Park Road , near Notting Hill Underground station

Kensington Road , near High Street Kensington Underground Station

Pont Street , near Knightsbridge Underground station

Russell Square , near Russell Square Underground station

Temple Place , near Temple Underground station

Thurloe Place , near South Kensington Underground station

Warwick Avenue , near Warwick Avenue Underground station

Wellington Place , near St. John's Wood Underground Station