Complex demolition in a sensitive neighbourhood had to be combined with temporary support engineering linked to the retained facade on Newgate Street and support of the double basement perimeter walls which had to be put in place prior to demolition of the supporting structure. Throughout the project the Post Office underground mail distribution tunnels had to be protected, monitored for movement, and sealed off, while the access shafts leading to ground level had to be isolated from the surrounding construction works and 'in filled'.
Archaeological remains were present, particularly in the area of the west building, which contained the 'Dickensian Comptor Prison'and the remains of the Roman wall and Bastion. The latter had to be maintained as a publicly accessible exhibit, and is now on show in the foyer of the new west building.
A number of ancient monuments and listed buildings surrounded the complex, requiring close liaison with English Heritage and the Museum of London, which maintained a presence on site throughout all the substructure works.