David Cameron has warned of a "global food crunch" as the era of abundant food supplies draws to an end.
Speaking at the centenary conference of the National Farmers Union, the Conservative leader set out a series of measures aimed at supporting homegrown farming.
He said that increasing competition for farm produce from the growing economies of China and India, the growing market for biofuels and the threat of global warming will all add to pressure on food supplies.
Britain must now treat food security as seriously as energy security, he said.
Cameron called for an end to production subsidies across Europe and a level playing field in agricultural regulations to help British farmers compete.
He said farmers must "reconnect with their customers" by wooing them away from supermarkets with organic delivery box schemes, farmers' markets and local shops.
"These three things, I believe, will help us face down the ever-growing threat to our food security."
Cameron told the conference in London that the UK's self-sufficiency in food has fallen from 72 per cent in 1996 to 60 per cent today.
He warned: "Just as we are relying - indeed, depending - more and more on foreign farmers to fill our shopping bags, cupboards and fridges... so the days of abundant food from around the world may well be coming to an end."
With Chinese consumers now eating more meat, farmers are switching from grain to livestock and causing a strain on global grain stocks, he said.
Climate change is reducing crop yields, while the switch to biofuels to tackle global warming leaves less land available for food production.
"These three factors - diet change, climate change, crop change - are contributing right now to global food crunch," he said.
The conference also heard from environment secretary Hilary Benn.
