Britain's Advertising Standards Authority has ordered Dyson not to repeat an ad that claims its vacuum cleaners don't rely on filters and don't clog. The ruling, which follows a complaint from competitor Hoover, comes despite Dyson having cleared its claims before running the ad. It also backed up the claim with independent evidence that its technology worked. As is often the case with ASA rulings, it came down to the regulator's belief that certain phrases would be misunderstood by consumers.In this case, it ruled that "a Dyson doesn't rely on a filter" would be interpreted by the general public to mean that there is no filter at all in Dyson's machine. While Dysons do contain filters, they perform auxiliary air intake and hypoallergenic functions, and do not need to be frequently cleaned. Most vacuum cleaners use filters to help remove dust from air, and they require frequent cleaning and replacement--Dysons use the eponymous inventor's cyclonic separation system. "We understood that neither the pre-motor nor the post-motor filters fitted in a Dyson cleaner were used in the primary separation of dust and dirt from the air," the ASA said in its ruling. "We recognised that Dyson had intended the claim to highlight the difference between the filtration system of Dyson cleaners and that of other cleaners ... We considered, however, that viewers were likely to understand the claim "a Dyson doesn't rely on a filter so there's nothing to clog" to imply Dyson cleaners did not have a filter, which meant they could not become clogged, although we appreciated that this was not the message Dyson had intended to convey." The ruling all but admits that the Advertising Standards Authority evaluates complaints based not on the technical accuracy of a claim, but on whether a complainant's misinterpretation of it was "likely" -- even if other branches of Britain's advertising regulatory system had specifically blessed the claim at hand. "The Broadcasting Advertising Clearance Centre (BACC) said they sought expert advice from a consultant and discussed the ad in their secretariat meeting before clearing it. They said they agreed with Dyson's argument that, although the ad stated "a Dyson doesn't rely on a filter", it was not misleading, because it did not state that there was no filter at all," it wrote. "We noted the expert commissioned by the BACC had accepted Dyson's evidence that the suction power of certain Dyson cleaners remained constant when the dust collection bin filled up with certain quantities of dust," According to the ruling, the ad must not be run again in its current form.