Up to two-fifths of a crop of fruit or vegetables can be wasted because it is "ugly", a report on food waste has shown.

Produce grown in the UK that does not meet retailer standards on size or shape or is blemished is often used for animal feed or simply ploughed back into the ground even though it is edible, with as much as 40% of a crop rejected.

The report, commissioned by the UK's global food security programme, also showed that the average household throws away more than 5kg (11lbs) of food a week, and nearly two-thirds of that waste is avoidable.

The waste costs £480 a year per household on average, and £680 per family.

Households throw away a fifth of the food they buy, wasting it for reasons ranging from cooking and preparing too much food to not using it in time before it goes off, the study showed.

Consumption and initial production are the areas where the majority of food is wasted in the UK, the study said.

Retailers respond to demands by consumers for high-quality food by imposing standards that can lead to much of the crop being wasted, but some progress is being made with supermarkets marketing "odd shapes and sizes" for fruit and vegetables.

There is also growing evidence that more UK consumers are prepared to accept "ugly" fruit and vegetables, amid concerns over sustainability and increasing food prices, the research said.

In developing countries, much of the loss of food occurs during post-harvesting storage, processing and packaging.

Tackling waste globally is a major part of the action needed to provide enough food to feed a growing world population sustainably and tackle hunger, which affects one in eight people worldwide, the report said.

Around a third of food produced globally is lost or wasted.

Prof Tim Benton, an expert on Food Security at the University of Leeds, said: "Over 5 million people in the UK live in deep poverty, where basic food provision is a daily challenge.

"Nearly 400,000 people needed support from food banks last year, according to the Trussell Trust.

"At the same time, 15m tonnes of food is wasted annually, with nearly half discarded within UK households. Reducing the scale of losses and waste throughout the entire food system is a crucial step towards improving global food security."

The report highlights priorities for research to help reduce food waste, including improving harvesting and packaging technologies, good seasonal weather prediction and new ways to reduce food waste within the home.