Britain will become a net importer of wheat for the first time in a decade this year because of bad weather.
The National Farmers Union said more than two million tonnes of wheat had been lost because of last year's poor summer. Prolonged cold weather will also hit this autumn's harvest.
But NFU president Peter Kendall said the shortage was unlikely to affect the price of bread because of the global nature of the market.
He told the BBC Today programme the average yield fell from 7.8 tonnes a hectare to 6.7 tonnes last summer.
Looking ahead to the 2013 harvest, Mr Kendall said farmers had managed to get only three quarters of the planned wheat planted this year.
"If we got three quarters of the area planted, and the same yield as last year, we could be looking at a crop of only 11 million tonnes of wheat when we actually need 14.5 million tonnes of wheat for our own domestic use here in the UK," he said.
"We have got to put it in context,'' he added. ''This is only the first time since the late 1970s that we have been net importers, Over the past five or six years we have been in surplus."
Mr Kendall said only about 10% of the cost of a loaf of was attributable to wheat. The rest was due to processing, transport, and packaging, he said.