Phil Stride, Head of Thames Tideway Tunnel at Thames Water, said:
“We support the type of measures Philadelphia is seeking to put in place.
“They could help extend the life of the Thames Tideway Tunnel, but in no way replace the need for it. This is because London has a far bigger population and much less open space than Philadelphia. The capital’s sewers, which have evolved over many decades, are integral to the city’s drainage and are already operating close to capacity.
“Unlike Philadelphia, London also sits mostly on impermeable clay and saturated gravels, akin to a sponge already full of water. Even if there were sufficient space available, diverted rainwater simply would not drain away quickly enough between storms, risking flooding across the capital.
“The maximum practical level of retrofitting the Philadelphia approach across London would take over 30 years to implement, cost an estimated £13 billion and cause untold traffic disruption. Also, they would not sufficiently control the sewage discharges the tunnel needs to intercept.
“Years of independent study have confirmed that the Thames Tideway Tunnel is the most cost effective way of solving this unacceptable pollution.”