Somerfield said yesterday that it had enjoyed an “exceptional” Christmas as Waitrose became the first supermarket rival to break cover and admit it would be interested in buying some of the chain's 955 stores.

Mark Price, Waitrose managing director, ruled out a £2.5billion bid for Somerfield but said he would be interested in picking up some sites.“ There is no doubt about our ambition to grow Waitrose and if the right stores came up we'd be interested in buying them,” Mr Price told The Times.

Somerfield, owned by a private-equity consortium that includes Robert Tchenguiz, has appointed Citigroup to hold an auction for the group. Information packs have been sent to potential bidders.

The Christmas trading figures surprised the City. Somerfield, Britain's fifth-biggest supermarket chain, said that like-for-like sales rose 6.7 per cent in the three weeks to January 5.

Paul Mason, chief executive, said that Somerfield had outperformed the industry's average growth rate for 12 of the past 16 weeks. “Somerfield has enjoyed an exceptional Christmas. Our strong like-for-like sales growth reflects the turnaround in the business and our clear focus on delivering the local grocery offer our customers want,” Mr Mason said.

The figures contradict rumours about the health of the Somerfield business given fierce competition among the four largest chains. TNS, the research specialist, said that Somerfield's market share had fallen to 3.7 per cent in the final 12 weeks of 2007 against 3.9 per cent the year before.

Somerfield generates nearly £4.5billion of annual sales and a deal would help one of the major supermarkets close the gap on market leader Tesco.

Details of the sale are thought to have been sent to every player in the market, including Marks & Spencer, Waitrose, Aldi, Lidl and the Co-op.

Mr Mason has focused on turning Somerfield into the “favourite local grocery shop”, moving it away from direct competition with the likes of Tesco and Asda.

He said: “Somerfield is well positioned to take advantage of its great store locations. We are delighted with the progress in the business.”

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