This hole is 4 Inch (100mm) in diameter and was probably drilled before the actual pipe run was put in place and a new hole was drilled later. Unfortunately, the hole has been used by rats to get into the cavity (the gap between the outside brickwork and the inner one can be seen here) and, once in the cavity, the loft space as well as the under floor area become pathways that rats can use.
Solution
The redundant hole needs to be patched up (‘proofed’) to stop any further access and then a program of trapping indoors to ensure there’s no rodents within the fabric of the building.
