WORK is due to start next week on upgrading the local sewage works revealed as the worst treatment site in the area for spilling effluent into streams and rivers.

Horsell environmental campaigner Andrew McManus spotlighted the sewage-spill problem with a protest in the River Bourne where it flows through the Heather Farm nature reserve, about a mile from Chobham sewage works.

Following the protest, where he was joined by local councillor John Morley and featured in the News & Mail, Thames Water announced on its website that it intends to begin work on planned “short-term” improvements on Monday.

No details have been provided of the upgrade for the site in Broadford Lane – which discharged effluent into the River Bourne 98 times in 2021, for a total of 1,140 hours.

The Thames Water announcement says it will be working five days a week at Chobham, with the work due to be finished by 20 December 2023.

Its improvements follow a national outcry at the release of untreated sewage into rivers and the sea during periods of heavy rainfall. Storage tanks become overwhelmed by the quantity of rainwater and effluent from sewers running into them and automatically discharge surplus liquid.

Mr McManus said the “appalling state” of the discharges was due to underinvestment by Thames Water, poor regulation by the Environment Agency and Government inaction. He will be lobbying Woking borough councillors tonight, as they arrive for the monthly full meeting of the council, to call Thames Water to account for the discharges.

Surrey Heath MP Michael Gove has also expressed alarm at the Chobham works overflows, and has requested an urgent meeting with Thames Water to discuss spillages into the Bourne.

“I am very concerned by the discharges, and I have just written to both the Environment Secretary and to the chief executive of the Environment Agency to ask for their assistance in preventing them,” he told the News & Mail this week.

Thames Water was asked for details of the work to be done at Chobham but had not replied at the time of going to press. A spokesperson for the company did, however, confirm claims that raw sewage had flowed out of the works and through the perimeter fence in the summer.

“There was a pollution incident at Chobham Sewage Treatment Works on the 25 August, due to the combination of a blocked inlet screen and a summer storm. Unfortunately, this led sewage to overflow on to the site and to pass through the fence.

“Our teams worked with the neighbouring farm to clear the sewage away. We would like to apologise to local people for this incident.”