Grocery giant Asda posted its first sales fall in four years as chairman Andy Bond said he expected "conditions to remain tough for some time".
The company, owned by US giant Wal-Mart, is the first of the "big four" supermarket chains to see comparative sales slide into the red on sales.
In the three months to 31 March sales, excluding fuel and VAT, were down 0.3%.
Asda, with 374 stores and 170,000 staff in the UK, is to create 300 jobs at a home shopping centre in north London.
The firm said first-quarter profits grew ahead of sales and beat internal targets, but it did not give any figures.
It also unveiled a £12m investment in frontline services to reduce queues and assist customers.
Rising food inflation has been hitting sales growth amid increased competition between the big four, which also includes Tesco, Sainsbury's and Morrisons.
British consumer price inflation jumped to a 17-month high in April, driven in part by higher prices for food.
Mr Bond said: "The market has slowed down significantly since the turn of the year, and I expect conditions to remain tough for some time."