More than 900 million tonnes of food is thrown away every year, according to a global report.

The UN Environment Programme‘s Food Waste Index revealed that 17% of the food available to consumers – in shops, households and restaurants – goes directly into the bin.

Some 60% of that waste is in the home.

The lockdown appears to have had a surprising impact – at least in the UK – by reducing domestic food waste.

Sustainability charity Wrap, the UN’s partner organisation on this report, says people have been planning their shopping and their meals more carefully.

And in an effort to build on that, well-known chefs have been enlisted to inspire less wasteful kitchen habits.

The report has highlighted a global problem that is “much bigger than previously estimated,” Richard Swannell from Wrap told BBC News.

“The 923 million tonnes of food being wasted each year would fill 23 million 40-tonne trucks. Bumper-to-bumper, enough to circle the Earth seven times.”

It is an issue previously considered to be a problem almost exclusive to richer countries – with consumers simply buying more than they could eat – but this research found “substantial” food waste “everywhere it looked”.

There are gaps in the findings that could reveal how the scale of the problem varies in low- and high-income countries. The report, for example, could not distinguish between “involuntary” and “voluntary” waste.

“We haven’t looked deeper [at this issue] but in low-income countries, the cold chain is not fully assured because of lack of access to energy,” Martina Otto from Unep told BBC News.

The data to distinguish between the waste of edible food and inedible parts – like bones and shells – was only available for high-income countries. Lower-income countries, Ms Otto pointed out, were likely to be wasting much less edible food.

But the end result, she said, was that the world was “just throwing away all the resources used to make that food”.

Ahead of major global climate and biodiversity summits later this year, Unep executive director Inger Andersen is pushing for countries to commit to combatting waste – halving it by 2030.

“If we want to get serious about tackling climate change, nature and biodiversity loss, and pollution and waste, businesses, governments and citizens around the world have to do their part to reduce food waste,” she said.

Richard Swannell pointed out: “Wasted food is responsible for 8-10% of greenhouse gas emissions, so if food waste was a country, it would be the third-biggest emitter of greenhouse gases on the planet.”

In the UK, the average household could save £700 per year, according to Wrap research, by buying only the food they ate.

Where food waste is voluntary, the Covid-19 lockdown appears to have had the surprising effect of revealing precisely how it can be remedied.

According to research by Wrap, planning, careful storage and batch-cooking during the lockdown reduced people’s reported levels of food waste by 22% compared with 2019.

“Being confined to our homes has resulted in an increase in behaviours such as batch cooking and meal planning,” the charity said. “But the latest insights suggest that food waste levels are likely to rise again as we emerge from lockdown.”

In an effort to avoid that, well-known cooks and chefs have lent their names and social media profiles to the campaign against kitchen waste.

British TV cook Nadiya Hussain is working with Wrap and offering tips and leftovers recipes via Instagram. And Italian restaurateur Massimo Bottura, chef patron of Modena eatery Osteria Francescana, which has three Michelin stars, has been appointed Unep goodwill ambassador “in the fight against food waste and loss”.

Throughout the lockdown in Italy, his family produced an online cooking show called Kitchen Quarantine, encouraging people to “see the invisible potential” in every ingredient.

While millions of tonnes of food was thrown away, an estimated 690 million people were affected by hunger in 2019. That number is expected to rise sharply in the wake of the pandemic.

Ms Andersen pointed out that tackling waste “would cut greenhouse gas emissions, slow the destruction of nature through land conversion and pollution, enhance the availability of food and thus reduce hunger and save money at a time of global recession”.