Tankers were seen “rushing to deliver tens of thousands of litres of raw sewage” to a River Chess plant.

People near Thames Water's Chesham Sewage Treatment Works noticed there were at times six tankers, reportedly able to carry 30,000 litres of raw sewage, queued outside the plant last week.

Some locals complained to Thames about the large vehicles travelling at anti-social hours and going too fast or behaving inconsiderately as they travelled into Chesham.

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The Berkhamsted works had recently pumped sewage into the Grand Union Canal for three hours, on the morning of March 2.

It is believed that following a fault in Berkhamsted, the tankers had been transporting hundreds of thousands of litres of sewage to Chesham, where there was spare capacity, to avoid pumping it into the canal.

The fault apparently ended up taking three days to resolve.

Paul Jennings from the River Chess Association said the tankers may have averted a much greater environmental impact.

He added that Thames Water has reportedly apologised for issues caused — but maintains the fleet of tankers was necessary to protect the environment.

The company has been contacted for further comment.