The BBC's Robert Pigott: "The government is under pressure to intervene"

It already suspects that farming families are being pushed to breaking point by what they claim is a crisis in the beef and sheep industries.

In some cases, incomes have fallen by about three-quarters in the past two years, says the NFU.

More than 80,000 farmers will be asked how they are being affected in an attempt to press the government into action.

On the rack: The BSE crisis hit farmers

It comes after a weekend of increasing political ferment over agriculture, during which it emerged that the Labour-dominated administrations in Scotland and Wales were planning to seek extra government handouts for hard-pressed sheep farmers.

Agriculture Minister Nick Brown ruled out cash aid, but Ross Finnie, the Liberal Democrat farming minister in the Labour-Lib Dem Scottish coalition, said that he would be pressing for extra money when Mr Brown meets him and his Welsh counterpart Christine Gwyther on 8 September

The NFU claims that farmers are facing the worst crisis since the 1930s with incomes in some instances falling 75%.

NFU President Ben Gill said: "Times have been extremely hard for farmers over the past few years, but an increasing number of farmers are now facing desperation."

The NFU blames a number of factors including the BSE scare and the drying up of Russia as a market after the onset of its currency and economic crisis.

Aid scrapped

Before the 1996 BSE ban nearly all of these calves had been exported to Europe for veal production, which ended in Britain in the 1980s. Now at the end of the calving season, they suddenly have no value.

Earlier this month the government scrapped the calf processing aid scheme, which gave payments to slaughterhouses and farmers to dispose of the 600,000 unwanted calves born every year to British dairy cows.

Pig farmers have had to spend £250m to comply with the UK ban on stall and tether systems - currently there is no similar legislation in the rest of Europe.

Sheep dumped

News of the audit comes in the wake of claims that farmers were losing money on livestock.

Henry Aubrey-Fletcher: "We have the finest, most wholesome food in the whole of Europe"

Last week, Welsh sheep farmers dumped 355 ewes at an RSPCA centre in Colwyn Bay, saying they could no longer afford to keep them.

Henry Aubrey-Fletcher, who owns a 1200-acre dairy, beef and arable farm in Buckinghamshire told the BBC it was time for the farming industry to start promoting British products as quality products.

He said: "We were hit hard by the BSE crisis and a lot of confidence was lost in our products.

"But now, with new controls in place, we have some of the best food in Europe.

"We have got to start talking it up and telling everyone how brilliant it is."