The main problem with all the subsidence is the number of lorries and delivery vehicles which have been allowed to drive over the pedestrianised areas. When the pedestrianisation was rushed through back in 1990/1991 (remember that?), little thought was given to the impact of hundreds/thousands of vehicle movements over the brickwork. In addition, the advent of the German market and the weight of that has added to the deterioration of the pavements.
They will have to put down a very strong sub-base now to ensure that these vehicles don't create subsidence again.
This was also the reason for redoing Centenary Square as the square was used by heavy cranes etc for the Big Wheel, ice rinks, etc. In the case of Centenary Square I just hope that it is strong enough to support those enormous structures. PS - I hate seeing them taking over the Square for 2/3 months of the year! Bah humbug!