Sainsbury’s sales were down 0.2% in the 12 weeks to June 17 and its market share fell 0.4 percentage points to 15.6%, researcher Kantar Worldpanel said.

Shares in the group, which in April agreed to buy third-largest chain Asda for 7.3 billion pounds ($9.7 billion), were down 1.8% at 9.14am local time.

Sainsbury’s is due to publish a first quarter trading update on July 4.

In contrast, sales at Asda, the British arm of Walmart, rose 1.8%. They were up 1.4% at market leader Tesco and up 1.9% at fourth-ranked Morrisons.

However, all three continued to lose market share to discounters Aldi and Lidl.

Aldi’s sales rose 8.2% and Lidl’s were up 10%, giving market shares of 7.4% and 5.4% respectively.

Overall, UK grocery sales rose 2.1% in the period, reflecting strong sales of spirits, soft drinks and hay fever remedies.

Kantar Worldpanel said grocery inflation was 1.9%, with prices rising fastest in markets such as butter, sodas and canned fish.