It is a hidden part of London people only have indirect contact with when they flush the toilet or navigate roadworks.

But groups were given a rare tour last week by Thames Water of the underground network of pipes that form the Wick Lane sewers.

Starting at Abbey Mills pumping station in Stratford, the nervous visitors were given full body suits, safety helmets and harnesses before descending into the unknown.

The aim of the trip was for people to gain an insight into the examples of Sir Joseph Bazalgette’s Victorian engineering - and to show how far the system has aged.

Stuart White, from Thames Water, was among those to take the trip.

He said: “It is not every day you get the chance to go down a sewer.

“After the safety briefing – make sure you wash your hands and shower as soon as possible afterwards – we were hooked up to a wire and told to climb down the ladder about 20ft into the depths.

“We were shown around the flood relief tunnel because of high levels in the main tunnel from recent rainfall.

“The ground underneath was slushy, dark and I didn’t dare ask what.”

Sewer operators Thames Water consulted earlier this year on proposals to build a new Thames Tunnel to revamp the capital’s sewers.

Main construction is due to begin in 2016, just as tunnelling for Crossrail is finishing.

More than 400 people are currently working on developing the detailed proposals for the project, including engineers involved in site investigation work along the tunnel’s proposed route.

Contractors are working on the Lee Tunnel, which being built to tackle flows from Abbey Mills.

Mr White said the tour proved was a useful look at how the structure works.

He added: “It was fascinating, the fact the system is still so efficient, but once is enough. I was quite relieved to get back above ground.

“The sewer flushers do an incredible job and I would have taken my hat off to them had I not been in the dripping bowels of east London.”