The package forms part of Thames Water’s wider plan to upgrade more than 250 sewage treatment and sewer sites between 2025 and 2030.

Costain will split delivery into eastern and western regions, each led by a regional senior project manager.

Eastern sites cover Barkway, Brentwood, Long Reach, Little Hallingbury, North Weald and Standon.

The western programme includes Aldershot, Burghfield, Esher, Horley, Lightwater, Marlborough, Northleach, Waddesdon and Windsor.

Work will include modernising inlet stations, strengthening the resilience of storm tanks and carrying out repairs, modifications and upgrades to wastewater systems.

Costain water sector director Matt Bateman said: “We’ll work closely with Thames Water and our supply chain partners to deliver these essential infrastructure upgrades, that will build resilience into the region’s critical wastewater system, efficiently and safely.”

Costain has previously delivered treatment asset upgrades for Thames Water at Markyate, Brickendon, Sandhurst and Selborne.

The contractor has also been carrying out clay compaction trials for Thames Water’s planned White Horse Reservoir in Oxfordshire.