Britons are throwing away 720m eggs every year – three times more than in 2008 and at a cost of £139m – according to research.

The scale of waste has been blamed on overcautious consumers relying on best-before dates to decide if eggs are fresh enough to eat, and the growing popularity of vegetarian and “flexitarian” diets has boosted overall sales.

Last year sales of eggs in the UK were 7.2bn – a 4% rise on the previous year – according to recent figures from the British Egg Industry Council.

But consumer research from the company behind the food waste app Too Good To Go, published on Tuesday, revealed that UK households binned 720m eggs last year, compared with 241m in 2008 according to Wrap, the government’s waste advisory body.

The research also showed that 29% of Britons throw away eggs solely because they are past their best before date. However, eggs are often still good and safe to eat long after the date on the packaging has passed. EU legislation requires that the maximum best before date on eggs must be 28 days from when they were laid.

The research found that just 23% of Britons were familiar with the water test that reveals whether eggs are still fresh enough to eat. If eggs sink to the bottom of a bowl of cold water and lie flat on their sides, they are very fresh. If they are less fresh but still good to eat, they will stand on one end at the bottom. If they float to the surface, they are no longer fresh enough to eat. This is because as the egg gets older, the size of the air sac inside increases, making it float.

“If you’ve been throwing your eggs in the bin based on the dates on the box, you’ve probably been wasting perfectly good food,” said Jamie Crummie, the co-founder of Too Good To Go. “Food waste is a huge problem – a third of all food produced globally is wasted. Small changes from each of us can make a big difference.”

Too Good To Go is challenging the British public to use the water bowl test to check the freshness of their eggs to help cut down on edible food needlessly being binned. Meanwhile, research by Wrap has shown that 20% of people don’t realise that it is possible to freeze eggs.

It has been suggested that dietary trends popularised by celebrities such as Joe Wicks have reinvigorated egg sales. In addition, the spike in egg consumption may be partly due to a change in advice from the Food Standards Agency in 2017 – almost 30 years after the UK salmonella crisis – stating that pregnant women, babies and elderly people could safely eat runny or even raw eggs.

Egg producers believe the rise in the number of eggs being wasted could be down to consumers’ ignorance and thoughtlessness, and their view of eggs as a low-value item, unlike fresh meat or fish.

Yet they can be a useful ingredient in combating food waste. A British Egg Information Service spokesperson said: “Because eggs are naturally versatile and can turn leftovers into quick and nutritious meals in minutes, they can make a big difference to the amount of food people end up throwing away.”