Especially in the London area it is important that you seek advice beforehand if you wish to place a Peregrine Falcon nest box on a new structure/building. One reason for this is that modern buildings/structures are not always suitable for Nest Boxes or Trays aimed at encouraging Peregrines to breed.
Another reason is that Peregrines are highly territorial all year round and will not tolerate another nesting pair too close by. They can be very aggressive and if an attempt is made to place new pair too close, serious clashes and fights will ensue, disrupting the breeding cycle and quite possibly leading to the breeding failure of both pairs.
In many areas, pairs will have become “established” over the years and have maybe attracted expenditure to accommodate them. At some locations, CCTV may even have been provided. Disruption of such a site can obviously be avoided by discussion about positioning nest boxes.