It found that Hoover was the only brand with below-average reliability for its fridge-freezers, washer-dryers, tumble-dryers and washing machines. Hoover was also one of the brands that owners would be least likely to recommend to a friend.

A Hoover washing machine was more than three times more likely to need a repair in the first six years than a Bosch or Miele. Hoover also keeps washer-dryer repairers busy; 42 per cent of its machines needed fixing during the past six years.

Dyson also fared badly in the Which? survey of more than 14,000 people. The manufacturer came bottom of the reliability league for both its cylinder and upright vacuum cleaners.

In 2001 one in five Dyson upright cleaners up to six years old needed repair. Now that figure was nearly one in three. A Dyson cylinder cleaner was also five times more likely to go wrong than a Miele model.

Bosch and Miele were the brands least likely to break down — and the ones that owners were most likely to recommend.

Malcolm Coles, editor of Which? magazine, said: “Bosch and Miele are brands you can trust and they’re not going to leave you with dishwashers full of dirty dishes or vacs that won’t suck. On the other hand, you simply can’t rely on Dyson and Hoover to be reliable.”

A spokeswoman for Dyson said: “We’re puzzled by the recent Which? report. We closely monitor the reliability of Dyson machines and our bestselling machine, DC14, has a reliability rate of 98 per cent (the 2 per cent are missing manuals or tools). Our biggest retailer, Currys, confirms that reliability rates for Dyson machines are very high.”

A spokeswoman for Hoover said the company had no comment to make.

Which? also warns consumers against buying extended warranties for new home appliances. It says they are often more expensive than using the manufacturer’s guarantee and then paying for additional repairs. Which? found that the average cost of repairing a washing machine was about £30, while it cost about £114 to buy a three-year extended warranty for the watchdog’s bestbuy a Siemens WXL146A.

The Which? report said: “For a warranty to be of value, a machine would probably have to break down more than three times during the warranty period. That’s very unlikely.”

In another Which? report parents were urged to avoid ten child car seats that it had declared inadequate two years ago. Although the seats met minimum legal standards, Which? said they either would not offer enough protection in a severe crash or were difficult to install, and would therefore increase the risk of injury in an accident.

Mr Coles said: “We asked the manufacturers why they still sell these inferior seats, but some just hid behind the regulations, while others failed to answer our questions.”

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