Drainage in Kenilworth is unusual in that the foul side is generally straightforward and the surface water side is not.
The reason is plot size. A large villa with a large roof and a large area of hard surfacing produces a great deal of water in a downpour, and on these plots it is frequently dealt with by soakaway rather than by a connection. Soakaways have rules that get ignored: they need to be a sensible distance from the building they serve and from any boundary, they need ground that will actually accept water at a useful rate, and they need sizing against the area draining into them rather than against what will fit in the hole.
Trees complicate it further here. A soakaway sited under a mature canopy is both a root problem and a performance problem, and on a plot where every tree is protected the siting is a design decision made early rather than a hole dug where there is space.
A percolation test costs very little against a soakaway that fills in October and stays full until spring, and we test rather than assume.
Where a run belongs to the water company, building over or near it needs consent before the concrete goes in. Our drainage work page covers surveys, repairs and new connections.