Fat, oil and grease are clogging sewers at a cost of more than £11 million a year.

The number of blockages in Brighton and Hove’s sewers has risen from 6,400 to 11,700 between 2010 and last year – a rise of 83%.

Southern Water’s director of communications, Geoff Loader, said: “We are seeing more and more flooding in the UK caused by extreme weather and the effects of this can bemuch worse if sewers are blocked by fat and other products like wipes, nappies and cotton buds.”

Tours of the city’s sewers are enjoyed by more than 2,000 people between May and September each year.

They are designed to encourage businesses and householders to dispose of their cooking fats in an environmentally-friendly way.

Mr Loader said: “We do these tours because people are fascinated by what’s down here – it’s like a secret underground world.

“We hope to provide some information about the sewer system’s history and how we operate it today and get across a message about the importance of avoiding oil, fat, grease, nappies and sanitary products.”

The Victorians designed and built the sewers so well that they are still in use today.

Up until the 1800s, household sewage drained into cesspools at the back of people’s houses.

It wasn’t until 1860 that the town council decided to build a sewage system that would drain into the sea.

The labyrinth hidden under the city is made up of 300 miles of brick-built sewers that deal with 22 million gallons of sewage every day, plus a giant storm tunnel to contain flooding during heavy rainfall.

Mr Loader added: “Our aim is to try to keep the public sewerage system clear and running by encouraging our customers to bag it and bin it.

“This is why we urge businesses and householders to dispose of these items responsibly and urge other organisations to follow suit.

“There are sewers which are really big but ultimately, most are just a few inches in diameter.

“It really doesn’t take huge amounts to cause blockages but it’s expensive to clear the pipes and you put yourself at risk of flooding your homes and damaging the environment.”

No Brighton and Hove water drains directly into the sea before it has been treated.

For more information and to book a tour visit www.sewertours.southernwater.

co.uk