Sales at Asda's US parent company Wal-Mart increased 11.8% in September to $31.2bn.

The retail giant also said that like-for-like sales during the month had increased 1.3%, with year-on-year sales growth of 1.8%.

However, the year-on-year growth was much less than analysts had predicted - they had estimated growth nearer 2.2%.

A spokeswoman for Wal-Mart said that the company's sales in September 2005 were tough to beat because they were boosted by preparation for and recovery from Hurricane Katrina.

Meanwhile, Wal-Mart has rolled out a $4 generic prescription programme in Florida four months earlier than planned.

The programme allows people in Florida access to 314 generic prescriptions for $4.

Lee Scott, president and CEO of Wal-Mart, said: “The programme enables us to respond to the needs of our customers who have struggled far too long with the high cost of prescriptions.”