The Government will push water companies to cut sewage overflow into rivers in a U-turn to avoid defeat ahead of Cop26.

       Measures to reduce untreated sewage dumps will become part of the Environment Bill, with the Government reversing its earlier stance as it faced a rebellion from MPs on the eve of the landmark climate conference, which starts on Sunday in Glasgow.

       Ministers had previously argued that the "legal duty" to cut the spills, originally introduced by the Duke of Wellington in the House of Lords, would be too expensive.

       But on Tuesday evening it announced that it would place a duty on companies to "take all reasonable steps to ensure untreated sewage is not discharged from storm overflows into inland and coastal waters".

       The proposed compromise succeeded in winning over Conservative rebels who voted against the Government on the issue in the Commons last week.

       Philip Dunne, who had led the call from the Tory benches for tougher action against sewage dumping, welcomed the minister's amendment.

       "It provides a duty on water companies to progressively reduce harm from sewage, which is what I was looking for," Mr Dunne said. "I'm very pleased the Government has found a way to do that."

       The conciliatory amendment advanced by the Government puts a legal duty on water companies to make progress, but leaves out a clause that would have placed liability on the state.

       A Government source told The Telegraph: "We have listened very carefully. The debate in the Commons highlighted great strength of feeling. We want to clean up water quality, of course we do. This is a good middle ground and a pragmatic way of doing it."

       Raw sewage spills happen when rainwater mixed with waste from households and businesses is released into rivers and the sea.

       This is supposed to happen only in "exceptional" situations as the system becomes overwhelmed following particularly wet weather, but it has now become routine, with 400,000 releases last year.

       The cost of upgrading Britain's sewer system to reduce the spills is expected to be passed on to bill payers, though experts said estimates of a price tag in the hundreds of billions of dollars were too high.

       Analysis in a paper commissioned by the Government is expected to suggest that ending all spills of untreated sewage would cost between ￡338 billion and ￡593 billion – adding ￡1,000 to the average household bill.

       But restricting the overflows only when they are affecting river quality would cost significantly less, at between ￡9.9 billion and ￡15.7 billion, adding between ￡17 and ￡27 to annual bills.

       'Nobody is proposing digging up our entire sewerage network'

       Campaigners said the change would not mean replacing all sewers, with investment required in a smaller number of problem locations.

       Charity The Rivers Trust said "eye-watering" estimates of the cost were "scaremongering", adding: "Nobody is proposing digging up our entire sewerage network and starting from scratch."

       Mark Lloyd, the chief executive, said there "probably would be some increase in bills", but added: "Certainly, some of the figures that are being buffeted around in response to the Twitter storm are much higher than would be the case in reality."

       Luke Pollard MP, Labour's Shadow Environment Secretary, said: "Having spent the past few days defending their position, this screeching u-turn will do little to convince the public that the health of our rivers, rather than the health of Conservative polling, is at the forefront of ministers’ minds

       "The Government still has no clear plan and no grip on the issue of raw sewage being pumped into our seas and rivers."