The extension to the Northern line came a step closer to completion over the Christmas period as the first passenger trains completed journeys through the new tunnels.
Test trains entered the 3.2km of new track at Kennington, passing through Nine Elms station before arriving at the extension’s second new station at Battersea Power Station.
The trial journeys came ahead of the scheduled opening of the extension in the autumn this year.
Work is now focused on completing necessary signalling software and fitting out the two new Tube stations.
Heidi Alexander, deputy mayor for transport, said: “I’m delighted that the Northern Line Extension has reached this major milestone, with the project on track to welcome its first passengers in the autumn.
“Last year was one of the hardest in TfL’s history so it’s great to start 2021 on a positive footing, not least because the extension will support thousands of new jobs and homes for our city.”
The project is the first major Tube line extension since the Jubilee line in the late 1990s and marks the first addition of new stations to the Northern line since the extension to Morden in 1926.
When completed, it will bring Battersea and surrounding areas to within 15 minutes of the City and West End.
It is also expected to support around 25,000 new jobs and 20,000 new homes.
But the project comes at a torrid time for TfL, which has suffered a collapse in passenger numbers as a result of the Covid-19 crisis.
The capital’s transport network received £3.4bn in government support last year following fraught negotiations between the two sides.
But deputy mayor Alexander has warned TfL would need a further £2.9bn of emergency funding to keep services running in 2021.