Clearer labelling is needed to help people to buy genuinely British food, Conservative leader David Cameron says.
Mr Cameron says there has been a rise in "food patriotism"
At present foreign produce processed in the UK can be labelled as British, he told the Oxford Farming Conference.
He said "food patriotism" was on the rise and backed a "buy British" policy for the £1.8bn of food bought each year for schools, hospitals and the Army.
Meanwhile Environment Secretary David Miliband urged farmers to grow more crops that can be used as biofuels.
Mr Cameron told the conference that consumers "can find it difficult to back British farmers, because of inadequate labelling".
He called it "completely wrong" that food "can be imported to Britain, processed here, and subsequently labelled in a way that suggests it's genuinely British".
He said more people were buying British, and said government policy should make it easier for people to set up farmers' markets and farm shops.
And he said it was a "scandal" that the government, which spends £1.8bn a year on food for the public sector, did not measure the success of its attempts to encourage public bodies to buy food locally.
Gareth Edwards-Jones, a professor of agriculture at the University of Wales, told the BBC's World at One programme locally produced food might not be as "green" as imported goods:
"Some people suggest that it's actually more carbon efficient to grow tomatoes in Spain, where it's nice and hot, and import them to Britain, than it is to grow them in Britain, where we have to heat the greenhouses."
Speaking at the same conference, Mr Miliband said opportunities would arise for farmers as more consumers switch to biofuels - fuels which are "greener" and typically derived from certain crops.
He said while global warming created problems, it also created new markets and opportunities which farmers needed to grasp.
But he warned that those who caused pollution, including those involved in agriculture of import and export, would have to pay.
UK farmers will have a chance to become leaders in the field of "green" agriculture, he said.
"Every part of our economy will have to change dramatically if we are to live within our environmental limits. Farming as a sector is no exception."
But National Farmers' Union president Peter Kendall said farmers were already thinking about green issues.
"There's over four-million hectares now in agri-environment schemes and I think farmers are very aware of their environmental responsibilities," he said.
Better labelling of British food would be great - I try to only buy British food where the item otherwise has to be flown in. Peppers are a good example - I would rather buy frozen peppers or go without if British peppers are unavailable - but it is often difficult to tell the origin of loose produce. Flowers are another one - it's often impossible to tell where they're from and it's unreasonable to fly in a purely luxury item. And the treatment of British farmers is indeed shocking: the government would apparently be happy for us to have no farming infrastructure - which would be a very worrying position, especially if there is a major war.
I think that this is great! To be able to support our farmers who would grow our food and keep the countryside for produce. Not only would the environment benefit from less importing due to emissions (as the food is not travelling far to be consumed and we are not buying it from a continent half way around the world when it can be grown in this country), but also lift rural economies and unemployment, bringing back more farming and craft skills that are sadly lacking.
Mr D W, Cirencester, Cotswolds
I welcome Cameron's ideas but there are two other factors that should appear on food labels: food miles (the distance that the food has travelled and the resultant carbon footprint), and recycling information. The UK supermarkets are dreadful examples of how centralised delivery processes cause unnecessary transportation, and recycling information is essential for the UK to meet its landfill reduction aims.
Al Cale, Herts, UK