Sainsbury's has come under attack for vaunting the

provenance of its regional lamb while selling it at the same price as standard meat.

Following the launch of West Country lamb in south west stores earlier this year, it has started selling Cotswold lamb sourced from a producer group in the area at more than 100 Midlands stores.

But even as the retailer was accepting plaudits from NFU president Peter Kendall at the Royal Show this week, it was attracting flak for the low prices it paid lamb producers.

The lamb lines, cut and packed by Randall Parker Foods, sell for the same prices as standard lamb and the farmers who produce it get paid no more, despite the product's longer maturation and strong provenance.

"Differentiation only works if everyone in the chain thinks they're being rewarded," warned Sir Don Curry, the government's sustainable farming mandarin, at the launch event, held at Sainsbury's stand at the Royal Show. "One of the players, often the farmer, will give up if they feel it's not worth their while."

Thomas Binns, NFU livestock board chairman, added: "Retailers have to be very careful to deliver after making a big announcement of his sort. Sainsbury's is one of those that has raised volumes of imported lamb this year."

Randall Parker Foods said consumers would be put off buying at the meat counter if prices were higher.

"It's important that we get English lamb back on to the counter," said a spokeswoman. "We have pitched it at the same price as pre-pack to get the consumer to try it and see how good the quality is."

Price parity between regional and standard lamb had helped raise year-on-year sales of the West Country lamb lines by 20%, she added.

Sainsbury's plans to launch Downland lamb from Sussex in stores in the south east of England, and Moorland lamb in the north of the country. August demand is expected to hit a peak of 2,500 lambs per week through the programme.