Secrets of the London Underground

Tim Dunn and Siddy Holloway explore Earl's Court station – a busy interchange on the Piccadilly and District lines, it's a station that has always embraced innovation. It was the very first station to install a passenger escalator and the first to install automatic lifts. Tim discovers how even today, the station is embracing the modern, with a re-design of the walkways created to fit in with its famous glass roof.

Siddy visits Alperton, a classic example of the famous London Underground architect, Charles Holden, and the design was regarded as futuristic when it was built in the 1930s. And behind a locked door, Siddy reveals a hidden treasure – a legendary escalator originally built for and relocated from the Festival of Britain.

At the London Transport Museum depot, a dedicated volunteer shows Tim the restored inner workings of a 1930s platform indicator, which used a telegraph system to show passengers the destination of their next train.

Tim and Siddy go under the platforms of Paddington station. It has five different tube lines running through it, with its oldest and newest lines opening 150 years apart.

Tim dusts off the old Mail Rail line which used to transport post under London to sorting offices across the capital, and Siddy discovers some former police cells underneath the platforms, and unearths what remains of the luggage carousels from when passengers on the Heathrow Express were allowed to check-in their luggage in the main station.

At Tottenham Court Road, Siddy reveals the huge changes to the station to accommodate the Elizabeth Line, and tells the story of how the station's iconic mosaic artwork was preserved during the works and takes us behind a locked door to uncover a floodgate installed as part of Britain's Cold War defences.

At the London Transport Museum depot, Tim meets a young tube driver, who's built up a large following on social media for her posts showing behind the scenes of her job.

Tim and Siddy explore the forgotten tunnels underneath one of Britain's busiest stations – Waterloo.

Tim gets a tour of a hidden world underneath the main concourse, which includes a former typing pool, a rifle range and a full-size snooker table gathering dust. Siddy discovers a floodgate which would have sealed the tunnel entrance during German bombing raids over London during the Second World War.

Siddy visits Marble Arch on the Central Line, and meets the artist who created an iconic series of enamel artwork on the platforms in the 1980s. Each depicts the Marble Arch in a different design, and they're still in pristine condition after 40 years. Siddy hears how the designs came about, and how the artist had to learn the intricate craft of working with enamel to realise her vision.

And at the depot of the London Transport Museum, Tim learns about the latest enamel signs still being made and used across the Underground network, including the signage for the new Windrush Line.

Rail historian, Tim Dunn and Siddy Holloway from the London Transport Museum, get exclusive access to explore South Kentish Town - a station once on the Northern Line, but abandoned more than a century ago. Tube trains still run through it, creating an eerie atmosphere and the spookiest sound they've ever heard in a tube station. They explore the disused passageways, reveal the ventilation shafts still working to keep air circulating on the Northern Line today, and tell the story of the passenger once stranded at the station after getting off a train by mistake.

At a secret location somewhere in zone 1, Siddy gets a behind the scenes tour of the London Underground Control Centre . It's the hi-tech mothership of the entire network, sitting in an enormous control room, running operations, power, policing and track access from one central hub. It includes a huge multi-screen display, which can show simultaneous live feeds from any of the 12,000 CCTV cameras on the underground.

At the London Transport Museum depot, Tim meets one of the underground's buskers to hear the secrets to her craft - from how you get a pitch to which songs work best at which stations.

Rail historian, Tim Dunn and Siddy Holloway from the London Transport Museum, reveal the incredible story of the Thames Tunnel - the first successful tunnel built under a major body of water anywhere in the world.?It was built by Brunel and his father - and not originally intended for trains - but today links Rotherhithe and Wapping stations. Without the Thames Tunnel, the London Underground as we know it wouldn't exist. Tim hears about the incredible engineering that made the tunnel possible - as well as the many failed attempts to get it right, including a major flood. Siddy walks the tracks in search of evidence of the tunnel's original construction, revealing a series of striking arches.

In Lambeth North, Siddy explores this classic Leslie Green station, one of the least used in zone 1. But it has a significant history as a shelter during the Second World War, and as a training base for London Transport workers, especially women drafted in to work on the tube during the war.

At the London Transport Museum depot, Tim gets the inside story on plans to extend the Bakerloo line into south east London - including the building of a brand new 21st century tunnel.

Tim Dunn and Siddy Holloway get privileged access to the vast maintenance depot at Ruislip, at the end of the Central Line. It's the nerve-centre for all the engineering that takes place on the tube, from routine track repairs to emergency engineering. Tim gets a demonstration of how tracks are replaced, as a crane lifts huge pre-assembled sections of railway track into place. Siddy gets in the driving seat of a machine that moves ballast into place under sleepers to hold the track in position.

At Warren Street, on the Northern and Victoria lines, Siddy explores the station's constant reinvention. It first opened in the early 1900s, was remodelled in the 1930s and then had a massive make-over in the 60s when the Victoria line arrived. There's plenty of evidence of its past - including exquisite original tiles in a former spiral stair shaft.

At the London Transport Museum depot, Tim meets a poet who has had her work chosen to appear as part of the 'Poems on the Underground' series. She tells Tim about the idea behind the poem - remembering helping her mum hang out the laundry when she was a child.

Tim Dunn and Siddy Holloway get incredible access to the maintenance depot at Northumberland Park in north London, responsible for looking after the entire fleet of Victoria Line trains. Tim meets the team checking all the carriages, and sees the incredible precision needed to finely shave the metal wheels to keep them running smoothly on the tracks. Siddy climbs the 1960s control tower and finds a vintage control panel still in working order, directing the points on the track to make sure each Victoria Line train coming into the depot goes to the right place.

Tim and Siddy get to ride on the private service that links the depot with Seven Sisters station - alighting at its mysterious third platform.

At Finsbury Park station on the Victoria and Piccadilly lines, Siddy does a night-time track walk to access the now-disused tunnel which was part of an early experiment to run large electric mainline trains on the tube.

At the London Transport Museum in Covent Garden, Tim meets museum's CEO to hear about the importance of design across the tube network, and they look at the bespoke designs for seating fabric across different underground lines.

Rail historian Tim Dunn and Siddy Holloway from the London Transport Museum, explore the rich history of Stockwell station on the Victoria Line. It was originally the terminus station for the City and South London Railway - the first ever deep level electric tube railway in the world, and the birth of the tube as we know it.?Tim finds evidence of a deep level shelter used by Londoners during the Second World War. On the platforms, he reveals something rather more contemporary - the tiles depicting a swan in homage to a local pub. As Siddy descends deep into the station, she finds metallic tiles on the walls and cast iron segments in a disused lift shaft, each crucial relics of their era.

Siddy visits the main depot for the Docklands Light Railway. She hears how they're developing new technology to alert them to any passengers on the tracks. And she gets an exclusive preview of their new fleet of trains, currently on test runs along the network.

Tim Dunn and Siddy Holloway meet at Gloucester Road in London's museum quarter - a station serving the Circle, District and Piccadilly lines.

Tim Dunn and Siddy Holloway explore the unusual station at Old Street, which serves both the Northern line and mainline trains.