Dyson has won a complaint about rival Miele concerning how to predict the lifespan of a vacuum cleaner.
A catalogue ad for a range of Miele vacuum cleaners said: "All Miele cylinder vacuums are tested to last for 20 years*", with the asterisk linking to a line stating: "Based on average usage of 45 minutes per week at maximum output."
Dyson challenged whether the claim that Miele cylinder vacuums were tested to last for 20 years was misleading and could be substantiated.
Miele told the Advertising Standards Authority (ASA) that there was no standard measure for 20 years' life of a vacuum cleaner and provided the watchdog with some, but not all, documents relating to its internal testing procedures.
The company acknowledged that the tests were not of the vacuum cleaner as a whole but of single parts of the product, but added that they demonstrated that an average life of 20 years was achievable based on 45 minutes' usage per week at the maximum output.
The ASA said consumers would interpret the claim to mean that it was very likely that Miele cylinder vacuums would still be working in 20 years' time.
"However, we considered it was unclear from the evidence provided whether Miele cylinder vacuums would last for 20 years in the home, or how likely it was that it would have a lifetime close to that figure.
"On that basis, we were concerned that we had not seen sufficient evidence to support the claim 'All Miele cylinder vacuums are tested to last for 20 years'."
It ruled that the ad must not appear again in its current form, adding: "We told Miele to ensure they held sufficient evidence to substantiate claims in future."