The union will launch the "Great British Food Brand" at a conference to be addressed by Agriculture Minister Nick Brown.

NFU president Ben Gill said it was vital that British products were associated with food safety and better quality.

He told BBC Two's Newsnight that this, combined with clear labelling, would increase much-needed sales for British farmers.

But he said competition from cheap imports meant many farmers were going out of business, and called for a "major change in pricing policy ... in the next few weeks".

Several supermarkets are supporting the NFU

The NFU, which says it represents most farmers in England and Wales, decided to promote British goods after a survey of 1,000 adults contacted at random.

It concluded that British shoppers want to buy British food, and 87% of people associate it with quality. But it said they often have difficulty in recognising it on supermarket shelves.

Asked to compare British food with the products of what the NFU calls "its principal foreign competitors - France, Germany, Thailand and Brazil", the UK was seen as top notch for safety, kindness to the environment, and animal welfare.

Jill Rawlins, from Somerfield supermarket, told Newsnight that "every effort would be made to support British farmers".

But she said a "careful equation of quality and price" had to be weighed up.

The campaign is the latest twist to the trade row started earlier this month when France defied EU law by maintaining its ban on British beef, saying it was still not safe from "mad cow disease".

Farmers' protest

It ignited on Monday night when French farmers in tractors blocked the freight terminal of the Channel Tunnel in Calais for two hours.

The blockade was a "symbolic protest" at a boycott of French goods by many British stores angry over France's hostility towards British beef.

The boycott was also prompted by revelations that French farmers have used human sewage in animal feed.

Prime Minister Tony Blair told his French counterpart Lionel Jospin on Tuesday that the ban on British beef was illegal.

But in a further sign of the worsening situation, the French agriculture minister Jean Glavany announced he was cancelling a planned visit to Mr Brown.

UK farmers are now planning to picket an education authority which buys French chicken, and French demonstrators in Calais are threatening fresh blockades of British goods.

The Conservative leader, William Hague, said the prime minister should "stick up for Britain" and ban imports of French meat.