The National Farmers' Union is mounting a major campaign to encourage supermarkets to do more to support British livestock farmers.

Letters asking buyers to make a range of best-practice pledges are to be sent out to the multiples.

"We're seeking to identify the areas where retailers are working proactively with livestock farmers," said Peter King, chief livestock adviser at the NFU, which backed the initiative at this week's NFU conference.

The aim was to celebrate good practice in the hope it would be taken up by other chains. "We're not trying to catch them out," said King.

Waitrose's work with producer groups as well as Tesco and Sainsbury's commitments to use British meat for their premium ranges were singled out for praise.

The exercise would also help clarify exactly what information retailers and abattoirs wanted from farmers, said King.

But farmers would have to make their own pledges in return if the idea were to work, he stressed.

"The campaign is almost a contract with the market. We have to encourage our members to produce what the market wants."

The move came as a dispute erupted at the conference between NFU president Peter Kendall and Sainsbury's chief executive Justin King over low milk prices.

Hailing their comments as "positive engagement in the supply chain", Peter King warned that similar arguments applied in the livestock sector.

"There's still a huge gap between what farmers are getting for their meat and the true cost of production without subsidies. The market is not yet ready to cover that cost."

The National Beef Association gave the NFU livestock campaign a cautious welcome. But low prices were still the biggest problem facing farmers, said chief executive Robert Forster.

"Our big disappointment is that the retailers are so closely bound on price competition they can't move prices up even if they want to," he said.