Diane Abbott, the shadow health secretary, said: “For years we have been told that flossing is an essential part of caring for our teeth and gums. Now it turns out that the only people really benefiting were the dental floss manufacturers. Yet another healthcare myth bites the dust.”

The NHS states on its website that dental floss “helps to prevent gum disease by getting rid of pieces of food and plaque from between your teeth” which can cause inflammation. But it warns that flossing incorrectly can damage the gums.

Last year journalists at AP news agency asked the departments of health and human services and agriculture in the US for their evidence that flossing works.

The government acknowledged the effectiveness of flossing had never been researched, and when the federal government issued its latest dietary guidelines this year, the flossing recommendation had been removed.

Journalists also looked at research conducted over the past decade, focusing on 25 studies that compared the use of a toothbrush with a combination of brushing and flossing.

The findings showed that evidence for flossing is ‘weak, very unreliable,’ of ‘very low’ quality, with ‘a moderate to large potential for bias.’