Expert in rethink on Thames 'super-sewer' plan
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An expert who recommended London should have a £3.6bn "super-sewer" has said there may be a cheaper alternative involving two shorter tunnels.
Chris Binnie led a study group which in 2005 said one tunnel under the Thames, from Hammersmith to Beckton, was the best way to solve sewage dumping.
But he said a number of factors had changed since the research was done.
A second phase of consultation on the controversial 20-mile (32km) tunnel is due to start in the autumn.
Thames Water wants to build the tunnel to prevent raw sewage being discharged into the Thames after heavy rain.
But opponents have raised concerns over the impact of construction works on parks and house prices as well as the cost to Londoners.
Mr Binnie, former chairman of the Thames Tideway Strategic Study, believes building two shorter tunnels instead of one could save up to £1.5bn.
He said: "If a way could be found not to have to build that central bit [of the tunnel] and thereby save £1bn, I think it is worthwhile having that final look."
Mr Binnie said in the six years since the report was completed a number of things had progressed including the amount of sewage, improvements at sewage treatment works and the construction of the Lea Tunnel.
"It's important in my view for a major project like this to have one last look and see whether we really do need, under all the latest information, to actually commit to that," he said.
Thames Water said since the study in 2005, it had undertaken extensive work to verify the proposed tunnel was an essential part of the solution needed to tackle rising levels of raw sewage in the Thames.'Unacceptable risks '
A statement said: "We are clear that the proposed Thames Tunnel is the best, most cost effective way of making London's sewerage network fit for purpose in the 21st Century and beyond.
"More delay in progressing the scheme would create unacceptable risks for the river and everyone who uses it."
Hammersmith and Fulham Council, which is against the water firm's plan, said the comments by Mr Binnie "blows a major hole in all of Thames Water's arguments".
A council statement said: "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.
"There are cheaper, more effective and less disruptive options to clean up the river that need to be re-examined as a matter of urgency."
If approved, construction on the tunnel would begin in 2013 and be completed by 2020.