More than 4m hours of raw sewage discharges poured into rivers and seas last year, a 129% increase on the previous 12 months, new figures are expected to reveal on Wednesday.

Total discharges from the 14,000 storm overflows owned by English water companies that release untreated sewage into rivers and coastal waters increased by 59% to 477,972, making 2023 the worst year for sewage spills, according to an early estimate of the Environment Agency figures seen by the Guardian.

Senior industry sources were preparing for the government to turn its guns on water companies after the record year of discharges. The Environment Agency said it was setting up a whistleblowing hotline for people who work in the industry to report any activity that concerns them.

The heavy rainfall over the autumn and winter is likely to be blamed by the industry for the huge rise. Storm overflows are supposed to be used only in extreme weather but for many years they have been used routinely, discharging raw sewage even on dry days in some cases. The academic Peter Hammond has shown how water companies are routinely using storm overflow discharges in their water management.

This year, for the first time every storm overflow has been fitted with a monitor, known as an EDM, but the scale of the rise in discharges is beyond what full monitoring would be expected to provide.

The scale of releases into waterways comes as rivers in England are at crisis point, suffering from a toxic cocktail of raw and treated sewage pollution, chemical toxins and agricultural runoff.

The revelations will put pressure on the water industry and the government, whose plans to tackle storm overflows have been criticised for not going fast enough. The plan aims to eliminate only 40% of raw sewage overflows into rivers by 2040 and discharges would continue being released into waterways until 2050.

In the last few weeks ministers have engaged in a flurry of announcements in anticipation of the shocking data on record sewage spills.

These included an announcement of a £180m plan to fast-track action on sewage discharges, in the face of criticism not enough is being done.

The water industry wants to invest a record £96bn to the end of the decade to tackle sewage discharges, leaks and the impending water supply crisis but has been criticised for passing the costs on to customers for investment that should have been carried out years ago.

The regulator Ofwat has to decide whether to allow companies to increase water bills to pay for the investment. Some customers will face huge bill rises to pay for vital infrastructure work. Thames Water is seeking to raise bills the highest of any company, by 40 per cent. Ofwat is the ultimate arbiter of whether the industry will be allowed to pass the cost directly on to customers as they seek to tackle years of underinvestment and the pressure of extreme weather from climate change.

When the full data from every storm overflow in England is released by the Environment Agency on Wednesday, some rivers and seas are likely to be shown to be suffering hugely from sewage pollution.

As well as total discharges increasing from just over 301,000 in 2022, the average discharge per storm overflow has increased to almost 35, a 52% increase, suggesting huge surges in spills into some waterways.

More than 60 discharges a year from a storm overflow should spark an investigation by the Environment Agency. The agency is in the middle of a criminal investigation into potentially illegal discharges by water companies and the regulator Ofwat is investigating six firms for widespread illegal sewage dumping from treatment works via storm overflows.

Industry insiders said groundwater ingress into pipes is to blame for some of the scale of the discharges.

Figures from the Met Office show 2023 had four individual months within the top 10 wettest on record and the UK recorded its sixth wettest October since 1836 last year.

Met Office assessments said Storm Babet in the autumn brought the third wettest three-day period on record for England and Wales. In November Storm Ciarán was an exceptionally powerful storm, comparable to the Great Storm of 16 October 1987. Rainfall in the autumn of last year was 410mm, which is 122% of the 1991-2020 average.

Defra has been approached for comment.