An expert who once gave his backing to the Thames super sewer has dealt a huge blow to the project by arguing that the case has moved on and the plans should be “reconsidered”.

Independent consultant Chris Binnie’s original assessment in 2006 was used to validate Thames Water’s case that the �3.6 billion tunnel is the only viable option to reduce the amount of waste that flows into the river.

But last week he wrote to a commission into plans suggesting that a much shorter tunnel, when paired with the recently-built Lee Tunnel, may work just as well.

East End campaigners are vehemently against the super sewer as it would leave King Edward Memorial Park in Wapping unusable for several years.

The costs of the works have also soared since they were originally proposed and could add �10 a month for life onto the bills of all Thames Water customers.

In Mr Binnie’s evidence, he also accepted that the millions spent on researching the Thames Tunnel far outweighed that spent on other options.

Hammersmith and Fulham Council leader, Stephen Greenhalgh, whose authority is leading a assembly of councils against the plans, said Mr Binnie’s evidence “blows a major hole” in the utility giant’s arguments.

“Now is the time for Thames Water to start listening to the expert who was once on their payroll and go back to the drawing board,” he added.

Thames Water said it has undertaken “extensive further work” since Mr Binnie’s study.

It said a smaller tunnel would not work because existing sewers are too small to allow waste to pass through to the treatment works at Beckton quickly and would cause odour problems.

High rainfall would “completely overwhelm” another system, it added.

It insists that the super sewer is the most cost effective solution.