Responding to a Freedom of Information request, Transport for London (TfL) told the paper that seats on the District, Jubilee, Northern, Circle, Piccadilly, Metropolitan and Hammersmith and City lines are never shampooed.
The Bakerloo, Victoria and Central line get a wash once every six months.
However, before we get too grossed out, it's important to note that TfL says carriages get a clean every night back at the depot, with seats being brushed regularly and hoovered on a 21-day rotation.
Back in 2014, Time Out magazine carried out a test to see how dirty Tube seats are, and video shows clouds of dust (thought to be a combination of human skin and dirt from shoes) billowing out after they're hit with a rubber hammer.
Testers looked at the Piccadilly, Victoria, Northern, Bakerloo, Jubilee, Central, District, Circle, Hammersmith and City, and Metropolitan lines.
At the time, the Piccadilly line seemed to have the most dust coming out of its seats.
The London Underground's Chief Operating Officer, told the Independent back in 2014: "Over four million journeys take place every day across the Underground network.
"Our trains and stations are professionally cleaned throughout the day and night."
Beautiful train stations around the world
Beautiful train stations around the world
Whether you're catching a train or just looking for an iconic place to visit, New York's Grand Central Terminal is a must-see if you're in the city. The Main Concourse has been featured in countless TV programmes and films, and is as romantic in reality as it is on screen, with the ceiling displaying its famous mural of the constellations. Around the station you'll find shops, upscale restaurants and a branch of the New York Transit Museum. Don't miss the Whispering Gallery in front of the Oyster Bar restaurant where you and a friend can stand at opposite corners of the arched entryway and whisper into the corners to hear each other's voices as if you were standing next to each other! The Biltmore Room, also known as the Kissing Room, is located below the former Biltmore Hotel and is known as being the place where passengers would get off the train and greet their loved ones with hugs and kisses.
Mumbai's Chhatrapati Shivaji Terminus, once named Victoria Terminus after Queen Victoria, is one of India's most beautiful UNESCO World Heritage Sites and an architectural masterpiece, boasting a fusion of Victorian Gothic and traditional Indian style. As India's busiest railway station with millions of commuters using it every day, it serves suburban railway services and long distance trains. Don't miss the figures on top of the columns at the entry gates - the lion represents Britain and the tiger represents India.
The Sao Bento station in the city of Porto, Portugal is best known for its intricate tiles that adorn the walls of the vestibule. The 20,000 tiles dating from 1906 to 1916 were painted by Jorge Colaco, who was the most important azulejo painter at the time. They illustrate the evolution of transport and historical events in Portuguese life, such as the arrival of King John I and Philippa of Lancaster in Porto in 1387 and the Conquest of Ceuta in 1415. The 20th century station was built where the former Convent of Sao Bento de Ave-Maria was located and its glass and iron structure was designed by architect Marques da Silva.
Set in a valley on the banks of the Pipo River in the Tierra del Fuego National Park, Ushuaia Station is known as the End of the World station where prisoners were sent to labour camps in the 20th century. Today the station is popular with tourists who come to take in the spectacular views from the luxury steam train that leaves the station. The route takes passengers along the Pico Valley and the Cascada de la Macarena station to learn about the Yamana people. There's also a stop where you can climb to a viewpoint and get a closer look at the stunning surroundings.
One of the oldest and most beautiful train stations in Thailand, Hua Hin Railway Station is well worth a visit to see its pretty Royal Waiting Room, which used to welcome King Rama VI. The wooden building was originally a royal pavilion located in the Sanamchan Palace in Nakom Pathom and was moved to Hua Hin in 1968. The Thai-style design is similar to the Maruekkhathayawan Palace - another must-see attraction for taking photos in Hua Hin. Behind the station you'll find the Royal Hua Hin Golf Course, which was the first to be built in Thailand.
Image: takumi.412. Used under Creative Commons Licence CC BY 2.0.
With a striking mint-green exterior and large dome that was reportedly designed by Gustave Eiffel, the CFM Railway Station in the Mozambique capital of Maputo is a fine example of colonial-style architecture built in the 20th century. Historic steam locomotives are on show at the station and modern trains stop here daily. Be sure to check out the Chez Rangel jazz cafe inside the station, which is a popular night spot in the city. On most weekends you can enjoy live music or choose from the large collection of old jazz gramophone records.
Image: MauritsV. Used under Creative Commons Licence CC BY 2.0.
Looking for the train station with the most amazing view? Visit Mexico's Divisadero Barrancas, where the descent to the Urique River begins. The station is a stop off for the Copper Canyon train that takes passengers along one of the world's deepest canyons. Here you can admire the Tararecua, Urique and Del Cobre ravines, pose for photos at the canyon edge, and even try staring down into it, if you're brave enough! Be sure to grab a tortilla at the station once you've taken in the views - they're freshly cooked by Tarahumara Indians.
Turkey's busiest railway station Haydarpasa Terminal is also one of the country's architectural wonders, built on 1,100 wooden beams and surrounded by the sea on three sides. The neo-classical, castle-like structure in Istanbul's Kadikoy district was built in 1908 as a gift to the Sultan Abdulhamid II by his German ally Kaiser Wilhelm II. German and Italian stonemasons crafted the stunning facade, which consists of textured sandstone and a steep pitched roof. As well as welcoming passengers arriving in Istanbul from Anatolia, the station has its own ferry dock.
The futuristic design of the Tsuzumi Gate at Kanazawa Station caused controversy when it was unveiled in 2005, due to it clashing with the traditional architecture of one of Japan's best-preserved castle towns. The modern entrance designed in the style of a hand drum and the Motenashi Dome, which was also revealed in 2005, have been popular with photographers and tourists in Kanazawa. The fountain in front of the station is another must-see as it has a digital-style clock displaying the time using water to form the digits.
Ever seen a jungle in a train station? Head to Madrid's Atocha station, where you can check out its lush rainforest in an old cast-iron and glass building while you wait for your train leaving from the new terminal next door. The old terminal dates back to 1892 when it was redesigned by Alberto de Palacio Elissagne and Gustave Eiffel after a fire destroyed the original building. If relaxing among exotic trees and plants isn't enough, the historic building is also home to birds and turtles, shops, restaurants and a nightclub!