Britain faces a major food crisis unless urgent steps are taken to revive its flagging agricultural sector, warns one of the world's most influential thinktanks.

Following a week in which world leaders and the United Nations expressed deep concern about the prospect of global food shortages, Chatham House suggests there needs to be a major shake-up in the UK's supply chain if the country is to continue feeding itself.

Controversially, the report's authors claim the debate about the use of GM crops in the UK will have to be reopened if productivity is to be increased, a suggestion likely to spark anger from the green lobby.

They claim: "As part of the co-ordinated technological response, the debate over GM technology will need to be reopened. GM crops are cited by many food supply professionals as among the tools required in efforts to reconcile the maintenance of agricultural productivity with more sustainable and affordable food production." But they add: "The issue remains highly contentious."

The thinktank on international affairs also claims the UK's consumers must expect to pay significantly more for their food if they want the country to develop a long-term sustainable food policy.

The stark assessment is contained in a new report, Food Futures: Rethinking UK Strategy, published tomorrow. It carries a chilling warning that the UK cannot consider itself immune to what is happening in the global food system, and that recent spikes in commodity prices, which have caused misery for many consumers as the cost of living has soared, should not be considered as freak events.

Instead, the report's authors quote experts in the food supply chain who believe the prospect of the UK being hit by a crisis is "highly likely". The report claims: "What we had thought of as abundant food supply is anything but. Western societies, in particular, have tended to take their food supply for granted. The global system will reach breaking point unless action is taken."

An increasing focus on food security comes as international demand for meat, crops and dairy products inflates prices. The inflationary trend has had a major impact on the UK, whose increasing reliance on other countries for its food has made it vulnerable to price fluctuations. Less than half - 48% - of food consumed in the UK is produced here, according to the Department for the Environment, Food and Rural Affairs. Just under 30% comes from Europe and the rest from outside the EU.

Rapidly increasing demand from countries such as China, the increased cost of fuel, a rising world population and falling yields have conspired to send food prices shooting up.

Between June 2005 and June 2008, the global price of butter rose by 74%, chicken by 62%, US wheat by 120% and milk powder by 69%. The effect has been to hit the pockets of UK consumers far harder than in other European countries. In the UK, food-price inflation peaked at 12.8% in August last year, compared with 6.7% in France and 7.1% in the United States. It meant that a UK family that spent £100 a week on food in 2007 had to spend nearly £13 a week - or £665 a year - more in 2008 to consume the same basket of goods.

John Beddington, the chief scientific adviser to the government, observes: "We are going to have to expect to have - throughout the world and not just in the UK - higher food prices."

According to Chatham House, it is vital that consumer attitudes change if the UK is to develop a sustainable food policy. We throw away about a third of all food purchased - 6.7 million tonnes a year - of which more than half is edible.

An increasing global population, coupled with limited land for agricultural expansion, has placed a new focus on each country's use of resources. The Chatham House authors conducted a series of private workshops with representatives from the food industry and quangos, retailers, scientists and government officials before compiling their report. Those interviewed agreed that the recent softening of food prices was a "fragile peace" and warned that the future could see increased social division, with those on lower incomes hardest hit by price rises.

But it is the UK's vulnerability to international events that could quickly trigger the nightmare scenario for the government - a shortage of affordable food.

"A crisis could develop through some form of external 'shock', such as animal or crop disease, or extreme weather events," the report claims. "A global food crisis caused by harvest failure and food shortages could also impact directly on British interests through restrictions on trade and reduced availability of both agricultural commodities and key inputs to domestic food production."

Equally, the experts questioned said that they believed that even a sustained period of high global food prices could be enough to trigger a crisis in the UK.

Much of the blame in the report for the UK's increasing dependence on the outside world for its food supply is laid at the door of falling productivity levels on farms. The report's authors call for more money to fund farm expansion, agricultural innovation and skills.

But it recognises that there is also an increasingly vocal lobby calling on the government to address the power of supermarkets, whose ability to dictate terms to farmers has been blamed for many of them going out of business.

The report concludes: "There is a real potential for demand growth to outstrip increases in global food production. Effects on developing countries would be devastating. Developed countries will be affected, too. Expectations of abundant and ever cheaper food could come under strain. The UK can no longer afford to take its food supply for granted."