Southern Water is proposing to charge customers an extra £279 a year on their bills by 2030, documents from a focus group show.

Under the plans, which account for inflation, each household would have to pay on average 73% more by 2030 compared with today – a total of £759 a year.

During the five years of the plan, customers would have to find £959 more than if bills stayed at the same price as today.

A “least cost plan” is also being considered, which would save each household £10 by 2030 but some improvement works on reducing sewage spills, repeat flooding, climate adaptation and sewage infiltration would not be completed.

Southern Water said the options are not final but part of a wider programme of research before it submits its proposals to industry regulator Ofwat in October.

The company added the figures do not include discounts of least 45% to around 125,000 households in financial hardship.

Southern Water has been criticised over a series of wastewater releases in recent years and was named among the worst-performing companies by Ofwat in 2022.

In 2021, it was fined a record £90m for dumping billions of litres of raw sewage into the sea at 17 sites, with various spillages around the east Kent coast.

Last month, fed-up traders blasted the firm for pumping sewage into the sea over a dry weekend.

An overflow pipe discharged into bathing areas covering Herne Bay, Whitstable and Tankerton overnight on Friday May 26, with officials blaming a “technical failure” at a pumping station.

A “no bathing” warning was issued for Herne Bay’s beach by campaign group Surfers Against Sewage, which wanted to alert people to the spills.

Speaking about the proposals, Katy Taylor, chief customer officer of Southern Water, said: “We regularly listen to the views of customers from across our region when we plan future investment in our network, and we discuss the possible impacts on bills.

“We know our communities want to see us investing to improve our environmental outcomes and to do it wisely, but we also recognise the concerns about rising payments in the face of a cost-of-living crisis.

“This is why it is important we work together with our communities, in finding the right balance.”

Cat Hobbs is the director of We Own It, a group campaigning for public ownership of the water companies.

She said that, according to a poll of more than 4,000 people commissioned by her group, 69% support public ownership.

She went on: “This absolute scandal makes it crystal clear that our privatised water system is broken.

“No wonder people are outraged to the point of boycott. Instead of forcing customers to pay even more, it’s time to take Southern back into public ownership.

“Shareholders the other side of the world don’t care that beaches in southern England are covered in sewage.

“We should copy Scotland – investment by publicly-owned Scottish Water is 35% higher and rivers and seas are cleaner as a result.

“Water is the stuff of life, it should be run for people not profit.”