Asda has been hardest hit by shoppers cutting back and spending more in no-frills supermarkets such as Aldi and Lidl, new research suggests.
The Wal-Mart owned supermarket, which on Monday announced Simon King, its deputy chief executive, had stepped down with immediate effect, saw its share of the UK grocery market drop from 16.7% to 16.3% in the 12 weeks to June 13, according to data from Kantar Worldpanel.
Mr King had only joined Asda in January, having been head of a number of Tesco divisions and Panda Retail, the largest supermarket chain in Saudi Arabia.
Asda has lost out to a growing trend for people to do more of their basic shopping at discounters, Kantar director Edward Garner said.
The group's market share is now only a fraction ahead of Sainsbury's, which held its share steady at 16.2%, as the number two retailer behind Tesco, a position Asda has held almost continuously since 2004.
Its market share slipped after it posted only a 2.6% increase in sales over the past three months, well below Tesco's 4.9% and rivals Sainsbury's at 4.3% and Morrisons with 5.6%.
Discount stores Aldi and Lidl both held their market shares at record levels of 3.4% and 2.6% respectively, having posted growth of 18% year-on-year in total sales.
Mr Garner said most of the growth at the discount stores came from shoppers doing more of their basic shop at the chains, rather than new customers, though he added that Asda may also have been affected by the high petrol price as most of its shops are large, out-of-town sites.
Overall, total grocery sales rose by 4.7% over the 12 weeks period, with the run-up to the royal wedding seeing growth of 7.8%, but which dropped to 2.5% in the four weeks following.