The age of steam will return to the Tube later as the 150th anniversary of the start of London Underground services is marked.
Specially invited passengers will move off from Kensington Olympia Tube station in west London aboard a train pulled by Met Locomotive 1, which was built in 1898.
The passengers will be in the restored Metropolitan Railway carriage No 353, which was built in 1892, as well as a set of Chesham coaches on loan from the Bluebell Railway in Sussex.
Making up the train will be the No 12 Sarah Siddons - one of the world's oldest electric locomotives in service which was built in 1922.
The train will travel non-stop to Moorgate station in the City of London. But it will move at slow speed and will be visible passing through a number of stations en route, including Earl's Court, High Street Kensington, Bayswater, Paddington, Euston and King's Cross.
The train will reach Moorgate at 10.30am. Normal Tube services will be running at the same time.
Londoners will get a chance to see two more journeys as the steam train will travel on sold-out trips from Olympia to Moorgate and from Moorgate to Edgware Road.
Among further steam journeys to celebrate the anniversary will be those on Sunday January 20.
The first stretch of the world-famous network opened on January 9 1863 - between Paddington and Farringdon - when it was known as the Metropolitan Railway.