A massive tunnel should be built along the River Thames in an attempt to bring London’s sewage systems under control and out of the 19^th century, the government agrees.

The 30km long engineering project will cost at least £2 billion and stop the current flooding of the Thames with untreated effluent every time heavy rains occur.

Like many cities, London has a combined sewage system. This collects sewage as well as rainwater run-off from roads, roofs, pavements etc. This waste water is taken to sewage works where it is treated.

Currently the flood run-off takes untreated sewage into the Thames killing fish and reducing water quality some 60 times a year because the 19^th century-built sewer network cannot cope with sewage and rainwater runoff together. Without this deliberate action today's ever-increasing number of London homes would regularly be flooded and polluted.

Now, after much wrangling – and more to come – the government has given its blessing to plans for a single 30km long tunnel planned to intercept sewage and rain water discharges along the length of the river and transport the waste water for treatment in East London. It would be the largest such project ever undertaken in this country.

Environment minister Ian Pearson said: "I think most Londoners would be shocked to hear that, because of an historic but increasingly outdated sewer network, a huge amount of untreated sewage and rainwater is spilling into the Thames at least once week. This is unacceptable.”

"This tunnel is the right solution for London and for the environment. It will give us a 21st century River Thames that we can all be proud of."

Barbara Young, chief executive of the Environment Agency said: "This option offers the best value for money and the environment. It will cope with future development in London and climate change.”

"We also believe it is the only option that fully meets the requirements of the European Urban Waste Water Directive."

But the water regulator Ofwat remains concerned about the value for money water customers will see in terms of the health and environmental improvements it will deliver.

“The quality of the Thames Tideway has been much improved in recent years,” protested an Ofwat report. “Much more will be achieved by the substantial programme (around £400 million) already under way to upgrade the sewage treatment works serving London.”

“The scale and complexity of the proposed interceptor tunnel raise issues of planning, financing and construction risk.”

“Ofwat will need to discuss with Thames Water possible changes to the general financing regime.”

“The scheme is still at a very early stage. Preliminary estimates suggest that the peak impact on the annual average customer bill could be an increase of around £37. But it is possible that when the proposals and options for delivery have been fully evaluated and costed the consequences for bills could be significantly different, possibly higher, than those so far identified.”