The new formulation may wash whiter but according to Procter & Gamble, maker of the rival brand Ariel, it also rots clothes. Nonsense, says Lever Brothers - a subsidiary of Unilever - the company behind Persil, and it is consulting its lawyers about legal action.
The row started when a P & G executive was quoted in a Dutch newspaper claiming that the fabric washed in the new powder showed damage after just 24 washes. Rubbish, retorted Lever Brothers, brandishing knickers washed 380 times in the detergent to prove there were no holes.
'In laboratory conditions you can prove anything,' said a Lever Brothers spokeswoman. 'What better lab is there than a consumer's own home?' She added that the product had been tested by 60,000 people, who had notched up 3 million washes, and none had shown any signs of damage to fabric.
P & G was yesterday playing down the comments by the unnamed executive, while playing up its concern for its customers, until results of outside tests it has commissioned become available next month.
A spokeswoman said that P & G has known about the new technology - which involves a catalyst christened Accelerator - for years. 'They haven't mastered it like we have,' said Lever Brothers. 'They'd love to be able to match it and they haven't'
Much is at stake. The washing powder market in Britain is worth almost pounds 800m, and pounds 6bn across Europe, and P & G and Lever Brothers are in cut-throat competition for their share. Persil is the market leader in ordinary, 'big box' powders and liquids but Ariel has the dominant share in concentrated powders - and that is the market which is growing most quickly.
New formula Persil is intended to steal a bigger concentrate share - and Unilever is throwing serious money behind it. The promotional campaign, starting in mid-May, will cost pounds 25m in Britain and pounds 200m across Europe.