The Kennington to Moorgate branch of the Northern Line will be shut for 17 weeks from next January so TfL can finish its redevelopment of Bank station.
The £700m upgrade will see the station, one of London’s busiest, made 40 per cent larger.
Four of the eight stations on the Bank branch of the service will be closed as part of the ongoing renovations.
It will also improve links between the lines and step-free access, as well as a new entrance to the station on Cannon Street.
Thus far, 1.2km of new tunnels and 200,000 tonnes of material have been excavated from under the City of London.
The Northern Line parts of Elephant & Castle, Borough, London Bridge and Bank will be closed but other lines will still be running through the stations.
Trains will still run north from Moorgate and replacement buses are being brought in for the closed stretches of the line.
During the four month closure, which will end in mid-May, TfL will connect the new tunnels to the existing railway.
That involves filling in the existing southbound line and flipping the platform over to the other side of the station.
Once the closure is over, the new features will open one by one, starting in the late spring. The final step, the new Cannon Street ticket hall is expected to open at the end of September 2022.
To help mitigate the disruption from the closure, service on the Charing Cross branch of the Northern line will be enhanced, and a new bus route between Oval and the City will ensure that customers in south London are able to reach the area easily.
Stuart Harvey, director of major projects for TfL, said: “Bank station has a vital role to play in the recovery of London from the pandemic. The changes to the station will transform the experience of every customer that uses Bank and will help the City as it continues to recover and people return to the area.
“I am proud of the work our staff, our contractors and everyone associated with the project has put into this vital upgrade and I look forward to that work being complete next year, but I am sorry that this vital and complex work will cause disruption early next year.”
Construction of the project began back in 2016, and was delayed for one year back in 2017. Work also had to stop for nine weeks due to the pandemic.
In 2019, prior to the pandemic, 110,000 passengers used Bank station during the morning peak period, about 44,000 of whom were changing between the five lines it shares with Monument station.