LONDON (Dow Jones)--The U.K.'s biggest retailer by sales Tesco PLC's (TSCO.LN) U.K. grocery market share was held at steady 30.8% in the 12 weeks ended June 13, according to Kantar World Panel market share data Tuesday. The nation's second biggest retailer, Asda Group Ltd., saw its market share slip to 16.7% in the 12 week period from 16.8% a year earlier. Asda is a subsidiary of the world's biggest retailer Wal-Mart Store Inc. (WMT) of the U.S. J Sainsbury PLC (SBRY.LN) remained in third spot with a market share of 16.2% over the 12 week period to June 13 from 16.1% a year earlier, according to Kantar. William Morrison Supermarkets PLC (MRW.LN) saw its market share rise to 11.9% from 11.6% according to Kantar, which monitors the household grocery purchasing habits of 25,000 demographically representative households in the U.K. Discount retailers Netto and Lidl's market shares remained steady at 0.7% and 2.3% respectively, while Aldi's share rose slightly to 3.1%, from 2.9% a year earlier. "The figures demonstrate the ongoing premiumization of the grocery market, with shoppers continuing to trade up as the gloom of the recession tails off," Kantar said, adding that shoppers are reaching for premium ranges such as Tesco Finest and Morrisons' The Best. "Furthermore, Waitrose continues to see a remarkably consistent share growth from a low point of 3.6% in November 2008 to a current 4.2%," Kantar said. -By Ian Walker, Dow Jones Newswires; 44-20-7842-9296; [email protected] (END) Dow Jones Newswires June 22, 2010 09:19 ET (13:19 GMT)