Government MPs have come under fire on social media after blocking a House of Lords amendment that would have blocked all discharges of raw sewage into the sea or rivers.

But will their action really make rivers and the sea filthy and threaten the environment? We have been trying to find some answers to a complex issue.

Are water companies allowed to discharge raw sewage into the sea and rivers?

Not in the normal water management - but companies do have flood prevention schemes known as Combined Storm Outfalls (CSO) where surface water is diverted from the surface into sewers which can then overflow and end up discharging raw sewage, albeit diluted, into the sea or rivers.

Companies do have to take measures to minimise this and if there are recurring problems they can be ordered to take action or even taken to court and fined.

Could all raw sewage discharge be prevented?

In theory yes, but it would be very expensive because it would mean that sewerage systems (the pipes that carry waste water away) would have to be replaced in almost every city in the country.

The cost has been estimated at somewhere between £150bn and £650bn and the work would take years, if not decades. To put those figures into context, the UK government has so far spent £261bn on Covid relief.

Is the problem getting worse?

Yes. A combination of more developments and more extreme weather events with the potential to cause flooding means that the number of sewage discharges is increasing.

There have been an increasing number of serious events that have resulted in huge fines. Earlier this year Southern Water was fined £90m for nearly 7,000 breaches of rules on allowing raw sewage emissions across the south of England.

Thames Water which serves London has had to pay fines of £7m and £4m after illegal raw sewage emissions.

What is being done to reduce raw sewage?

Water companies have been told to draw up plans to reduce the amount of raw sewage they discharge - and the government has been told to come up with new regulations to force them to reduce raw sewage emissions. Both reports have to be published by September next year.

The companies will also have to draw up 25-year plans to show how they plan to reduce the amount of raw sewage they allow back into rivers and the sea in the longer term.

Companies are planning to spend £7.1bn on environmental improvements between 2020 and 2025, of which £3.1bn is on storm overflows.

Are Victorian sewers to blame for the problems?

Many of the CSOs were actually created in the 1960s and 1970s in a bid to prevent flooding problems on new housing estates and other developments - but in easing one set of problems the water authorities (which were then government bodies) created new ones by pushing excess surface water into sewers.

But some of the problems do date back to the creation of early sewerage systems during the Victorian era.

What has caused the current row?

The government's Environment Bill is currently going through the House of Lords where the Duke of Wellington, a descendant of the victor of Waterloo and who sits as a cross-bencher, put down an amendment seeking ban raw sewage emissions altogether.

That was passed by the House of Lords - but when it returned to the Commons on Thursday the Lords' decision was overturned despite a rebellion by 22 Conservative backbenchers.

What is being said about the raw sewage issue?

Suffolk's Conservative MPs backed the government and voted to remove the House of Lords amendment last week - contributing to a comfortable victory by 64 votes.

Since then they have received many e-mails protesting about the vote, and have come under fire on social media platforms like Twitter.

Ipswich MP Tom Hunt said: "I’ve seen media reports over the weekend that I am in favour of pumping sewage into rivers and seas: this is not the case. This is not something I want to see."

While he agreed in principle with the Lords amendment, the fact that it was uncosted meant he could not support it. The government's commitment to forcing companies to stop discharging raw sewage was more realistic.

Central Suffolk and North Ipswich MP Dr Dan Poulter agreed: "Direct action is already being taken through the Environment Bill and will require water companies to monitor the water quality impacts of their sewage discharges and to publish this information."

The decision by MPs was attacked by pressure group Surfers Against Sewage whose spokesman Hugo Tagholm said: “We believe the water companies need to cut into the dividends they make every year to restore our rivers and our coastlines.

“They haven’t got a right to destroy these spaces and need to take the ambitious steps to restore them and we need to make sure the industry is not putting their profits ahead of making our spaces safe.”

Anglian Water insisted it was working to reduce raw sewage emissions - its record is good compared to other companies. A statement from AW said: "CSOs act as a necessary safety valve in old sewerage systems, to protect homes and businesses from flooding during heavy rainfall.

"But as our climate changes and extreme weather is now commonplace, they are no longer fit for purpose. Water companies have a proven track record of investing in environmental protection and improvements since privatisation.

"We have been addressing CSOs over many years, tackling those that pose an environmental risk first, and working through the rest.

“We welcome the Environment Bill’s new provisions on storm overflows, and are keen for the Secretary of State to bring forward a plan to reduce discharges from storm overflows and reduce their impacts.”