Combine harvesters have been damaged in waterlogged fields
Food prices could rise further because exceptionally wet weather has led to delays in the harvest, industry experts have told the BBC.
Farmers say they are behind on gathering in crops and are using valuable fuel to dry them for storage.
In a bid to help, the government has temporarily relaxed rules banning farmers from using equipment on waterlogged soil to get to crops.
Other experts say plentiful worldwide supplies should keep prices stable.
Farmers say this growing season started well but torrential rain means harvesting has been delayed and in some areas only a tiny percentage of crops have been gathered.
In a statement, the National Farmers' Union said: "Farming is suffering because of record rainfalls that have been recorded in the last few months.
"Fields have been flooded and it has been impossible, in some parts of the country, to access crops.
"A poor harvest will impact on all sectors, not just grain, with a lack of fodder for animal feed, as well as having a knock-on effect in terms of planting for next year's crop.
"For wheat and barley, in particular, the harvest is both difficult and expensive in terms of gathering and drying wet, sodden crops."
Farmers are usually barred from using machinery on waterlogged soil by rules aimed at protecting fertile land.
But Environment Secretary Hilary Benn yesterday relaxed the restrictions until 4 October.
He said: "We need to do all we can to help the harvest and I hope this decision will go some way to assist farmers who have been most affected."
BBC environment correspondent Sarah Mukherjee said farmers across Britain are reporting damage to combine harvesters as they try to cut crops in waterlogged fields.
Water can be wrung out of grain by hand as it is so wet, and thousands of pounds is being spent on fuel to dry sodden crops.
The NFU also expects yield to be down by up to 10% because some grain has started to sprout.
Food prices in UK shops have risen by 8.3% since January, an index compiled for the BBC said last week.
Some in the industry say the wet harvest will inevitably mean further price rises to come.
But others say that, if the weather turns, the quantity and quality of the harvest could still be good.
Alex Waugh, director general of the National Association of British and Irish Millers, said it was too early to predict the effect on retail prices because the quality of grain was still being assessed.
"At this stage, we don't think it's a disaster but imports are likely to rise," he said.
While retail managers say falling global wheat prices should ease the pressure on consumers, Mr Waugh said imported wheat still cost an extra £30 per tonne.
Wheat is currently selling at £112 per tonne on the futures market.
Gordon Polson, director of the Federation of Bakers, said the wet harvest could result in poorer wheat with less protein.
"We may still have to import some milling wheat, but at present that has not been decided and no one is currently talking about price rises for bread," he added.
The food price index produced for the BBC last week showed meat and fish up 22.9% with fresh fruit and vegetables up 14.7%.
Retail analysts Verdict Research also found price rises of nearly 50% for some individual food items.
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