On Thursday, 12 October 2017 09:33:54 UTC+1, wrote:

Tunnelling at Bank? Whats this for? I thought all the crosstail tunnelling
was complete long ago.

As others have explained a very large project to add a lot of capacity to Bank Stn. Primarily covers the Northern Line in terms of platform capacity but also adds a new ticket hall on Cannon St and much more interchange capacity. Also makes the station fully accessible but not on the link to Monument IIRC.

Another new ticket hall, at Bloomberg Place, for the W&C Line is due to open at the end of this year. This will provide escalator and step free access to the W&C at Bank.

--
Paul C
via Google