Thames Water wants to build the sewer from west to east London to stop millions of tonnes of sewage leaking into the River Thames every year.
Construction work is due to start in 2013 and take seven years if Thames Water’s plans are approved giving a massive boost to the civil engineering industry
But the Thames Tunnel Commission, sponsored by Hammersmith and Fulham Council, will now examine whether the 20-mile tunnel is the best solution.
Opponents of the scheme have raised concerns during an initial consultation exercise over the impact of construction works on parks and house prices as well as the cost to Londoners.
Thames Water believe the tunnel is vital to cut pollution which kills fish, damages wildlife and poses a health hazard.
Lord Selborne, who will lead the team scrutinising the plans, said: “I welcome the opportunity to pose the questions that millions of water bill payers are starting to ask.
“The key question is whether this multi-billion pound project is the best solution to making the Thames cleaner or whether there are sensible alternatives that are cheaper, greener and less disruptive.”
Hammersmith and Fulham Council leader councillor Stephen Greenhalgh said: “Doing nothing is not an option, but we need to consider the possibility that there are better alternatives.
“It remains my view that an alternative hybrid scheme, involving a shorter tunnel, diversion of run-off rainwater and sustainable drainage as well as improved river water treatment should be revisited as a matter of urgency.”
Thames Water said alternative options would cost more, be more disruptive and not achieve the required environmental standards.
A spokesman said: “We agree that the unacceptable level of sewage discharges to the river must be resolved at minimum cost.
“So we welcome the appointment of this commission and we look forward to providing whatever information and assistance Lord Selborne and his colleagues may require.”