Tube stations are so much a part of the everyday lives of London's commuters that few bat an eyelid at the architecture they see on the way to and from work every day.
But many of these stations were ahead of their time when they were built. By combining architectural beauty with often ingenious functionality, they spoke loudly about the civic pride they espoused – and the ambitions of London Transport which they were manifestations of.
On Tuesday, English Heritage added these 16 stations to the 56 already on the Listed Buildings register. Each is important in their own way, as three experts on the Tube's history and heritage explain here:
Distinguishing features: Boasts double Doric columns on its facade, a telltale sign of architect Stanley Heap's work. Named Brent until the opening of the nearby shopping centre in 1976.
Expert's view: "A neat little Grecian building. Heaps gave things a classical style here. Its well mannered – it must have been an eye-opener in its day. It was really about taking civic architecture to the suburbs."
Mike Ashworth, design and heritage manager, London Underground
Distinguishing features: Leslie Green's Caledonian Road uses lifts to transport passengers straight to platform level. It is truly step-free.
Expert's view: "All Green's stations were floodlit at night to enhance the prominence of the new public transport system. The platforms are one of the few pairs with the original coloured, patterned tiling virtually intact. All 46 Green stations had a different tile pattern, said to aid recognition by regular passengers." Mike Horne, Tube writer and former TFL employee
Distinguishing features: This 1924 station by Stanley Heaps was intended to kickstart the development of the area and is integrated into the shops either side of it.
Expert's view: "Many of these stations show that good design is as much about function as it is about form. Subconsciously the average commuter probably enjoys the Doric columns – but consciously they definitely appreciate that the station's wide entrance takes them quickly out on to four key roads as well." Gareth Edwards, London Reconnections blog
Distinguishing features: The farthest station from Central London. It feels more like a rural halt – hence the water tower, signal box and gable station entrance.
Expert's view: "The thing that amazes me is you half expect the village doctor to be outside on his horse. It's so marvellous that we have these outlying rural services on the Underground. Our customers like that heritage. It's part of the feeling of that market town and it means a lot to the people of Chesham."
Distinguishing features: Another Leslie Green station, opened in 1906. A concrete block was added on top in the 1960s.
Expert's view: "Green was the architect brought in to design all 46 stations for the new London Tube lines, opened in 1906-07. The scale of the job meant that the stations were all designed to a similar formula. The generic design relied on putting a distinctive cladding around a then-novel, steel-framed structure which allowed commercial premises to be built above." Mike Horne
Distinguishing features: Belsize Park Station includes a Second World War air raid shelter which could accommodate 8,000 people in two giant tunnels. Seven more were built at other Tube stations.
Expert's view: "Belsize Park has the iconic red facade that can be seen on stations throughout the city. This is the work of Leslie Green, who designed over 50 stations in just four years. Green was under orders to make his stations distinctive but cheap, and at only 9 shillings (45p) a foot, the red fronting did exactly that." Gareth Edwards
Distinguishing features: A surface station with a big ticket hall curving gently inwards.
Expert's view: "Perivale's sweeping curves – both inside and out – give it a distinctly 1930s feel, but in reality, the outbreak of the Second World War meant it wasn't actually finished until 1947. In design terms it's the work of Brian Lewis, an Australian who designed several stations for the Central Line. Like Holden, he bought into the idea of 'bright open spaces' and the station still has an airy feel to it today." Gareth Edwards
Distinguishing features: The platform walls look original, with their vibrant coloured patterns. But in truth the whole thing is modern – the original tiling is underneath the new tiles.
Expert's view: "Another good example of Green's work in the early Edwardian period and the exterior of the surface building is in good repair. Inside the ticket hall there is virtually nothing original, the 1980s ticketing project having put paid to many of the surviving original fittings." Mike Horne
Oxford Circus north-east and north west
Distinguishing features: Originally two different stations. The NE building was designed by the Central London Railway's Harry Measures in 1900 in unglazed buff brick, and the NW building by Leslie Green in 1906 in his characteristic oxblood red Burmantofts tiling (see Chalk Farm). The two were combined in the 1920s.
Expert's view: "The Green building was built for the Baker Street & Waterloo Railway. The Bakerloo was eventually financed and finished by American tycoon Charles Yerkes, but the part-finished works at Oxford Circus were so unsatisfactory that the below-ground parts had to be completely rebuilt, giving the station the doubtful privilege of having been the only Underground station to be rebuilt before it actually opened.
Both stations were so busy they were soon equipped with escalators instead of lifts and the ticket halls were shifted into the basements freeing up most of the street level structures for conversion to shops. For a while the Oxford Circus escalators were the longest in the world." Mike Horne
Distinguishing features: An unusual flatiron shape which makes it look like a slice of cheesecake sitting on the Camden landscape.
Expert's view: "A classic example of Burmantofts tiling – a Leeds tile company. It was a house style. That tiling is very classically a tube station and even in abandoned stations like York Road, people can tell that a building was once a Tube station. The tiles were like Lego bricks and could be slotted into any shape. It's like a Dairylea triangle on this site." Mike Ashworth
St John's Wood
Distinguishing features: At the bottom of the escalators a bronze arm holds up the most charming Way Out sign on the network.
Expert's view: "The feel of the 1930s is intact. Like Southgate, it has bronze escalators and uplighters. It's fascinating and a really very calm environment. It wasn't designed to be fashionable. The use of very refined detail proved very durable, hard-wearing, easy to clean. I love the tiles at platform level. They were designed to break up the space and provide visual interest." Mike Ashworth
Distinguishing features: In west London, a lot of stations like this were built in partnership with the mainline railway companies. GWR were involved here. The enormous box on the roof looks like a radiator.
Expert's view: "It's unusual. It owes a lot to London Transport architectural practice – but there are subtle differences, like the brickwork. Simple, plain lines, no fancy detail. In a way it looks like a cinema. It's a focal point for the local community. Stations like this were built like beacons to attract people to them." Mike Ashworth
Distinguishing features: Redbridge looks more like a space station than a Tube station, and appeared preposterously modern when it opened in 1947. Features a blocky tower and circular ticket hall.
Expert's view: "It was delayed the best part of the decade by the War. The tunnels were already built and there was a secret factory there. Attention to detail – the miniature roundels and the round building, reassure passengers and tell them that they are on the Underground." Mike Ashworth
Distinguishing features: A long, curved frontage is the focal point of busy station. The Underground signs, or roundels, on the outside of the building are of the 1919 design.
Expert's view: "The work of Charles Holden, whose presence can be felt across the Underground. Holden's modernist designs are special because they aren't just architecturally impressive, but often also deeply practical. Wood Green was designed to handle larger passenger numbers than used it in the 1930s, for example – something no doubt appreciated today." Gareth Edwards
Distinguishing features: Closed in 1994 and is now only used for filming. It opened in 1907 as Strand – you can still see the old sign from the street.
Expert's view: "In the 1930s the station had the reputation of being the coolest on the Underground, as there were neither passengers nor trains to generate the heat that soon pervaded the other stations. During the Second World War the station temporarily closed – used for storage of treasures from the British Museum and as an air raid shelter." Mike Horne