With a clang, the sliding doors close on the makeshift elevator and we begin to crawl the wall of the biggest vertical shaft I’ve ever seen.
A 200-foot-deep, 60-foot-wide concrete tank dropping to a tunnel junction below, its epic scale looks like something I’ve only seen on film: Dune or Bond.
The reality is less glamorous. It will fill up with whatever we flush.
Sky News had rare access to the ‘super sewer’ or Thames Tideway as it is officially called.
He has three of these giant tanks along nearly 20 miles of tunnel, each wide enough to fit three double-decker buses side by side.
The total construction time will be nine years at a cost of around £4 billion: an expensive solution to an enormous problem.
In an average year, 39 million cubic meters of water contaminated with sewage is discharged into the River Thames.
London‘s Victorian sewers were built after the Great Stink of 1858, a river stench so bad that parliament was unable to convene.
They were engineering marvels of their time, but over 100 years later, a deliberate design decision has become a major failure.
Dirty water from our homes flows into the same pipes that carry rainwater that runs off roads and roofs. So the rains can overwhelm the system – especially as London has grown.
We have more people flushing toilets and more of these hard tile and asphalt surfaces. To prevent sewage from flowing back into homes, it is deliberately dumped into the river.
Lucy Webster, director of external affairs for Thames Tideway, told Sky News: “When they were designed this would have been a very, very rare event.
“But today, with all its development, with population growth, it’s a very regular occurrence. And pretty much whenever it rains to any significant degree in London, it spills straight into the River Thames.”
Rage over ‘undulating brown plumes’
The super sewer will collect these overflows and send the sewage to a treatment plant in Beckton, east London and, in a downpour, fill these huge tunnels. It’s like a new river network under London.
Every London household pays £18 a year for these costs – but polluted rivers and coasts are a national problem and, if tackled, this bill will spread.
Campaign group Surfers Against Sewage recorded 14,000 untreated spills last year and 700 incidents of human illness caused by sewage.
Swaying brown plumes in rivers and around our coasts have caused popular and political outcry.
This week the government announced plans to make it easier to fine water companies for sewer leaks and many activists say they should find the money to clean up their profits.
Read more on Sky News:
Criminal charges against Drax for exposure to dust have been dropped
British leek supply ‘sold out in April’ at last warning
Drought in Italy exposes footbridge on Lake Garda
But Alastair Chisholm, director of policy at the Chartered Institute of Water and Environmental Management, says no one is being realistic about the scale and cost of work across the country.
“Right now it looks like a car accident. We have activists berating the government. We have the government and other politicians screaming from the rooftops that they really want to punish the water companies.
“We have water companies needing to invest amounts of money that are potentially inaccessible to customers. There will have to be a real reckoning with reality. And I think that will happen over the next 12 months.”
Click to subscribe to ClimateCast wherever you get your podcasts
The price for removing sewage from our natural waterways is high, but nature is paying the price for doing nothing.
Chris Coode, from the healthy river pressure group Thames 21, has witnessed the result of large leaks.
“You have a big patch of sewage in the river, and as the bacteria break down the organic matter, they consume oxygen,” he explains.
“Then you’ll end up with huge areas of deoxygenated water. The fish can’t breathe, so you’ll see them sometimes on the edge, panting. And you could have thousands of dead fish.”