Washing powder adverts that capitalise on claims to environmental friendliness should be banned because they are untrue and distort the market, say scientists at Imperial College.

Many detergents are "phosphate-free" and are claimed to be less harmful to the environment. When phosphates reach rivers and lakes they fertilise the algae that live on the water surface. These proliferate (eutrophication), which prevents light getting through to the weeds underneath. The weeds die and decompose, using up oxygen dissolved in the water. As a result, underwater animals are deprived of food and shelter.

Gary Morse, environmental scientist at the college, has done a life cycle analysis on detergents. This maps the flow of energy, materials and waste from production to disposal. He has studied eutrophication in western European countries, including those that no longer use phosphate-based detergents.

Mr Morse's main conclusion is that removing phosphate detergents from the environment does nothing to decrease algae growth. This is because the amount of phosphate in the environment would have to be reduced by 90 per cent to reach the threshold level at which any effect would start. The maximum contribution that the detergents make to phosphate levels is 10-20 per cent.

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In European countries without phosphate detergents, he says: "Nowhere has it contributed to a decrease in The minimum way to control phosphates is to install water treatment plants that remove all phosphates, including those from agriculture and industry.

Producing compact powders, another attempt at green policy, cuts energy use by about a third because "filler" production is reduced. "But in terms of the global energy balance it is nothing."

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Mr Morse's work was partially funded by an industry organisation, Centre Europeen d'Etudes des Polyphosphates. But he denies being partisan: "You'd be best advised to go and buy the cheapest detergent that does the job."