capacity by 40%, at a cost of around £700million. The overall project – incorporating twelve new escalators, two new lifts and two moving walkways – included: A new southbound platform for the Northern line and conversion of the existing southbound platform to passenger circulation space. New direct passenger tunnel with moving walkways connecting the Northern line and Central line. New escalators between the Northern line and the DLR A new station entrance and ticket hall on Cannon Street, just east of St Mary Abchurch, with new escalators and step free access to the Northern line and DLR. Modernising the station to comply with contemporary fire and evacuation standards. Owing to the severe curvature of the Central line platforms, there is a substantial gap between the train and the platform. Because of this, no step-free access was currently proposed for the Central line, as the cost would be prohibitive and it would be difficult for passengers to use. TfL described the construction of the project as "intricate and complicated", with over 30 listed buildings in the historic City of London located above the tunnels. The new southbound Northern line tunnel was dug from a worksite on King William Street, using the underground spaces left over from the closed King William Street tube station. Former running tunnels have previously been used as circulation space at Angel and London Bridge stations. As part of the development of the scheme, TfL worked with potential bidders to improve the design of the station from TfL's original design. The design proposed in the winning bid by Dragados was 9.7% cheaper than the original design (saving TfL £60million), took ten months less time to construct than the original design (the proposed closure of the Northern line was also five weeks shorter), and the layout of the station was more efficient. This substantially improved the benefit–cost ratio by 45% to 3:5:1. Progress Following consultations in the early 2010s, and a Transport and Works Act Order in 2015, construction of the new Northern line tunnel began in April 2016, and was estimated to take six years. By July 2019, the project had reached the halfway stage. By October 2020, the majority of tunnelling work, around , had been completed, with around 200,000 tonnes of material excavated from beneath the City. By July 2021, installation of escalators was underway, as well as preparation work to connect to the new Northern