Tesco and Morrison sales declined over the past 12 weeks while Sainsbury and Asda achieved growth, Kantar Worldpanel revealed on Tuesday.Overall growth in the grocery market slowed to 1.7%, the lowest level in 11 years.Tesco's sales fell 3.1% year-on-year, giving it a market share of 29%, down from 30.5%. Sales at Morrison dropped 3.9%, bringing its market share down to 10.9% from 11.6%.Sainsbury's sales climbed 0.9%, but its market share fell to 16.5% from 16.7% a year ago. Asda's sales advanced 2.4% and it was the only leading grocer to increase market share, rising to 17.1% from 17%. Kantar said price cuts by the big four supermarkets had led to a drop in the level of grocery inflation to 1.2%, the lowest level since May 2010. The supermarkets cut prices in the face fierce competition from smaller discount stores such as Lidl and Aldi and premium grocers including Waitrose and Marks & Spencer. The report comes ahead of Tesco's first quarter interims on Wednesday. RD