Improvement works at Mogden sewage plant are finally beginning - but not everyone is convinced the project will end problems with the site.

Thames Water, which owns the site, this week announced that parts of Mogden’s western embankment are being cleared to allow a £150m expansion to begin in the spring.

The company claims the plan will enable the plant to treat more than 50 per cent more sewage than at present - significantly reducing the amount of storm sewage that overflows into the River Thames during heavy rainfall.

Last July 20,000 tonnes of sewage spilled into the river from a combined sewer overflow at Mogden, killing hundreds of fish, and there was a subsequent spill in November.

Twickenham MP Vince Cable admitted he was sceptical whether the latest development would give neighbours of the site much cause for celebration.

He said: “I welcome this news but what matters to people is that Thames Water have a grip on the odour problem from the plant.

“After Thames Water spent £50m on partial coverage we had terrible smells for several months at the end of last year.

“As long as these problems persist there will be great scepticism about future promises.”

There was an outcry when Mogden’s expansion was given the go-ahead by Hounslow Council last year. Mogden Residents' Action Group predicted odour problems will worsen as a result.

Richmond Park MP, Susan Kramer, who took Thames Water to task over last year’s spills, believes the preparatory work is “excellent” news for residents but claimed it should have been undertook sooner.

She said: “It is outrageous that in a modern city untreated, raw sewage is still allowed to flow into a stretch of river that so many people use and enjoy.”

Steve Shine, Thames Water’s chief operating officer, said: “Although our sewage works operate well under stable, dry weather conditions, in heavy rainfall excess flows pass through storm tanks, which provide a lower standard of treatment, and overflow into the tidal stretches of the River Thames - rather than having sewage back up on to the streets or even into people's homes.

“As well as significantly reducing sewage discharges, these improvements will help reduce odour at the site, as the use of storm tanks will be reduced during heavy rain, and new and existing equipment will be covered over.”

Thames Water is currently appealing against legal orders issued before Christmas, which were designed to stop unsavoury smells escaping from the site.