Poor harvests caused by the bad weather could damage farmers more than 2001's devastating foot-and-mouth outbreak, the government's rural adviser fears.
Heavy rain and storms have battered wheat crops
Lord Haskins said farmers expected to lose about £100 for each acre of land.
The north of England has been hardest hit, but farmers across Britain are suffering, he said.
He told BBC Radio 4's Farming Today that cereal farmers were suffering the same sort of losses as the livestock industry had three years ago.
"For arable farmers in a sense it is much worse because there is obviously no compensation from the government," he said.
Shadow Agriculture Secretary Tim Yeo has written to Environment Secretary Margaret Beckett, calling on her to press the EU to hand out advance payments to ease their plight.
In his letter Mr Yeo says "While I appreciate that there is little by way of direct aid that the government could provide, you could assist farmers with their cash flow problems...by bringing forward the arable payments due in December."
Only about half the wheat in the country has been harvested and entire fields of crops have been left to rot because of the summer's heavy rainfall.
Some farmers have been able to do some harvesting during brief pockets of fine weather, but the recent persistent rain has made even that small amount impossible.
Last year's dry weather provided a bumper harvest, but the havoc caused by this year's torrential storms could also stretch on into 2005 as seeds and soil become damaged as well, Farming Today reported.
This season's crops are not a write-off yet, but their quality is deteriorating with every rainy day.
The National Farmers' Union (NFU) says thousands of farmers in north-east England are being forced to stand by and watch crops being ruined in the waterlogged ground.
Heavy rain has plagued Britain this summer
The NFU says it is exploring options to tackle the worst affected areas, in which some farmers could lose tens of thousands of pounds.
And it may liaise with the Department for Environment, Food and Rural Affairs (Defra) to organise assistance.
An NFU spokesman said: "We are looking to facilitate any way for those farmers who have harvested to help those who have not been able to set up so far.
"We are also exploring, with Defra, the possibility of bringing forward assisted payments that farmers would normally receive throughout the year to cover the current difficulties."
These payments are European subsidies for farmers and issued via Defra.
A Defra spokesman said: "There is no doubt this is one of the wettest and slowest harvests on record.
"We share the concerns of farmers and, like them, we are hoping for a spell of sunny weather and an up-turn."
Lord Haskins predicts heavy losses
Paul Temple, 42, who farms at Driffield in Yorkshire, has suffered as a result of the weather.
He said: "This has been one of the worst summers that I can remember in over 20 years of farming. A wet July has been followed by an even wetter August.
"We are struggling to use combine harvesters and harvesting is proving to be extremely expensive because of the cost of drying crops."
Mr Temple, said he would usually expect work an average of 26 days in August, but added he would be "lucky" if the conditions would enable him to complete ten full days on the land.
"Land preparation for next year's crops are well behind. The fields are saturated and we are struggling to drive on the land, which is something I would usually associate with a wet winter rather than summer," Mr Temple added.