Good news for anyone on a tight budget or who hates catchy advertising jingles: washing machines don't necessarily live longer with Calgon.

The manufacturers of Calgon, which has a retail recommended price of £4.48 for 15 tablets, say it contains polycarboxylates to soften hard water, preventing limescale from forming and thereby stopping the impairment of the washing machine's performance and reducing the risk of it breaking down.

But consumer organisation Which? simulated three years' worth of washing and found no evidence that using Calgon extended the life of the washing machine in "normal" washing conditions.

Although Which? found that using Calgon did reduce the build-up of limescale in the machine, the small layer that built up when it wasn't being used was insufficient to affect the running of the machine or suggest future failure.

Which? also believes that images used in Calgon's advertising do not accurately reflect "normal" wash conditions. While Calgon adverts show the effect of washing at 60C, the most common washing temperature is 40C, and this was the temperature used to test Calgon's efficacy.

Which? said: "Using Calgon in every wash, the average person would spend £295 over the course of six to eight years – the time our expert believes it would take before a normal machine in an area with particularly hard water would require attention as a result of limescale build-up. This sum could pay for a brand new washing machine; and you'd expect to get plenty of change if you paid for a service, including removal of limescale."

Calgon told Which? it had research to back up its claims but couldn't share that evidence due to commercial sensitivity.

It said: "We were both surprised and disappointed to see the comments in the recent Which? report on washing machines regarding the use of water softeners such as Calgon. We found the report to be highly misleading.

"There is no dispute that the regular use of Calgon prevents limescale build-up in washing machines. Limescale build-up does cause problems, especially for users living in hard water areas. Calgon helps to protect all the parts of the machine that come into contact with water."