A key section of the Northern line will close for four months to allow a £700m upgrade of Bank station to be completed.
Transport for London on Monday set out a new timetable for a 17-week “blockade” of the line’s Bank branch between Moorgate and Kennington stations.
It will be closed from January 15 until mid-May next year – about six months later than planned, due to the Covid shutdown of TfL’s major projects last year.
This is likely to have the unfortunate effect of hampering what TfL bosses hope will be a return to pre-pandemic passenger numbers next year.
Passengers will start to benefit from the new station around Spring 2022 but it will take until September or October 2022 before the new entrance on Cannon Street is fully integrated.
There will also be a series of weekend closures this summer and Autumn between Moorgate and Kennington, including on July 31- August 1 and September 4-5.
TfL chiefs said the 17-week shutdown was “sequenced in” to the work schedule and could not be brought forward to affect fewer passengers.
TfL managing director for customers, communication and technology Vernon Everitt said: “While there is never a right time to do anything like this, the prize at the end of the day of a new ‘crown jewel’ that we will have in the centre of the city to attract people back to London... we believe is worth the disruption of a 17-week blockade.”
There will be more trains on the Charing Cross branch to increase capacity to and from central London from next January, and a new bus route will run between Oval and the City.
However there will be fewer trains than normal on the remainder of the Bank branch until the work is completed.
The work at Bank station, which together with Monument station was the third busiest interchange on the Underground pre-pandemic, includes a new southbound platform for the Northern line.
A new station entrance is being built at Cannon Street and three quarters of a mile of new tunnels have been dug.
Overall, the project will increase capacity at the station – one of the most complex on the Tube network – by 40 per cent and reduce the time it takes to change between lines. The overall cost has increased from an estimated £600m at the outset of the project.
There will be step-free access to the Northern line and improvements to the existing step-free access to the DLR.
The upgrade includes two new lifts, 12 escalators and two moving walkways between the Northern and Central lines.
The work, including excavating 200,000 tonnes of material, began in 2016 and has been done while allowing passengers to continue to use the station.
A 34m-deep shaft has been dug on the west side of London Bridge to facilitate access. Engineer Iain Smith said: “It’s like building your house through your letterbox.”
But TfL has been unable to create step-free access to the Central line because of the estimated £30m cost and the large gap between Central line trains and the curved Central line platform.
The part-closure of the Northern line will allow the new tunnels to be connected to the existing railway and enable the new station to be finished. The current southbound tunnel will be converted into a passenger concourse.
A new station entrance on Walbrook opened in November 2018 and enables easier access to the Waterloo & City line, which reopened last month after a 15-month shutdown caused by the pandemic.
Stuart Harvey, director of major projects for TfL, said: “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 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.”
Pre-pandemic, more than 120 million passengers a year used Bank and Monument stations, up almost 40 per cent in a decade.
It was the third busiest interchange on the Underground, with 50,000 passengers each morning switching trains. It was regarded by TfL as one of the “largest and most complicated subterranean railway complexes in the world”.
The Northern line was also the busiest line on the network with more than one million passengers on weekdays.
The £1.2bn Northern line extension to Battersea power station will open this September. All trains serving the extension will travel via Charing Cross. Passengers wanting the Bank branch will have to change at Kennington.