The average price of staple foods will more than double in the next 20 years, leading to an unprecedented reversal in human development, Oxfam has warned.

The world's poorest people, who spend up to 80% of their income of food, will be hit hardest according to the charity. It said the world is entering an era of permanent food crisis, which is likely to be accompanied by political unrest and will require radical reform of the international food system.

Research to be published on Wednesday forecasts international prices of staples such as maize could rise by as much as 180% by 2030, with half of that rise due to the impacts of climate change.

After decades of steady decline in the number of hungry people around the world, the numbers are rapidly increasing as demand outpaces food production. The average growth rate in agricultural yields has almost halved since 1990 and is set to decline to a fraction of 1% in the next decade.

A devastating combination of factors – climate change, depleting natural resources, a global scramble for land and water, the rush to turn food into biofuels, a growing global population, and changing diets – have created the conditions for an increase in deep poverty.

"We are sleepwalking towards an age of avoidable crisis," Oxfam's chief executive, Barbara Stocking, said. "One in seven people on the planet go hungry every day despite the fact that the world is capable of feeding everyone. The food system must be overhauled."

Oxfam called on the prime minister, David Cameron, and other G20 leaders to agree new rules to govern food markets. It wants greater regulation of commodities markets to contain volatility in prices.

It said global food reserves must be urgently increased and western governments must end biofuels policies that divert food to fuel for cars.

It also attacked excessive corporate concentration in the food sector, particularly in grain trading and in seed and agrochemicals.

The Oxfam report followed warnings from the UN last week that food prices are likely to hit new highs in the next few weeks, triggering unrest in developing countries. The average global price of cereals jumped by 71% to a new record in the year to April last month.

Drought in the major crop-growing areas of Europe and intense rain and tornadoes in the US have led to fears of shortfalls in this year's crops.

The World Bank warned last month that rising food prices have pushed 44 million people into poverty since last June.