Bread prices are set to rise because of poor crops and increased energy bills, bakers warn.
Rank Hovis, which owns eight mills, is increasing its flour prices by an average £29 per tonne next month.
And ADM Milling, which owns nine mills, is pushing up its flour prices by £28.75 per tonne. The two companies together are the biggest millers in the UK.
Experts said this would mean price rises of about 15 per cent to 20 per cent for major flour users.
The National Association of Master Bakers, which represents about 1,000 small UK bakeries, expects bread to go up by two to four pence per loaf.
Chief executive Gill Brooks said: "The small craft baker will be hit particularly hard.
"Little outlying villages and coastal areas where trade is seasonal will struggle a bit but they will have to do it."
A spokesman for Rank Hovis, which owns the Hovis brand and supplies own-brand bread to other stores, said the price of its bread was being kept under review.
Gordon Polson, director of the Federation of Bakers, told trade magazine The Grocer that bakers were also being directly affected by rising fuel costs.
"If there are increases in flour costs it is inevitable that these costs will have to be recovered," he said.
ADM Milling said its price rises were an "essential reaction" to rising energy, fuel and wheat costs.
MD Ian Pinner said: "This is the third year that we have had to accept increased energy costs which are now 30 per cent higher than in November 2005. In addition, global wheat markets have moved up sharply in reaction to supply and demand figures showing world stocks to be the lowest for 25 years."
Bad weather has caused wheat crop destruction in the Ukraine, Russia and North America.
UK wheat prices are now 15 per cent higher than in November 2005 because of global market factors, lower stocks and forecasts of further reduced supply, Mr Pinner added.