This is expected to result in stations including Waterloo, London Bridge, Tottenham Court Road and Embankment becoming much busier than normal – with passengers advised to “seek alternative routes” or travel outside peak times.
There will also be a reduced service between Camden Town and Moorgate, which will impact on Northern line trains to and from King’s Cross, Angel and Old Street.
But there will be a train every two minutes on the Charing Cross branch during peak hours.
A temporary new bus service, the 733, will run between Oval and Finsbury Square, in the heart of the Square Mile financial district, to offer an alternative route from south London.
There will also be weekend closures between Moorgate and Kennington ahead of the shutdown.
The changes at Bank station will increase its capacity by 40 per cent and provide step-free access to the Northern line and improved access to the DLR. There will also be a new entrance on Cannon Street, in addition to the entrance on Walbrook that opened in 2018.
The Northern line “blockade” will start on January 15 and last until mid-May. The station will then reopen but will not be fully finished until next Autumn.
TfL chiefs admit the closure will hamper the return to work as the pandemic eases but say they have no option but to press ahead to complete the project.
Andy Lord, managing director of London Underground, said: “The Bank Station capacity upgrade is a crucial project to support the City’s continued growth and success.
“We are encouraging affected customers to check their journeys before they travel by using Journey Planner or the TfL Go app, and suggest they try to retime their journeys, or take a different route by Tube, rail, bus, walking or cycling during this vital 17-week closure.
“I’d like to reassure everyone that we are doing everything possible to reduce the impact of this closure, with an increased service on the Charing Cross branch and a new bus route into the City. We will also use this closure to carry out maintenance and improvement work at other stations in order to minimise future disruption.”
Pre-pandemic, Bank and Monument stations were the third busiest interchange on the Underground, with more than 120 million passengers a year.
During the closure, the two new tunnels will be connected to the Tube, meaning the Northern lines gets a new southbound platform.
The upgrade also includes two new lifts, 12 escalators and two moving walkways between the Northern and Central lines.
Engineers will take advantage of the closure by also doing work at London Bridge, Borough and Elephant & Castle, which is awaiting an upgrade.
The Bank transformation began in 2016 and has been done while keeping the station open.