Asda, the British supermarket arm of the world's biggest retailer Walmart, has today reported a fall in underlying sales in the key Christmas quarter, echoing rivals in blaming a tough consumer backdrop. 

The group's attempt to combine with rival Sainsbury's was thwarted by Britain's competition regulator in April.

It said today that comparable sales, excluding petrol, fell 1.3% in its fiscal fourth quarter to December 31 - a deterioration from a third quarter decline of 0.5%. 

Asda also said its gross profit rate, or margin, decreased, reflecting strategic price investments, discounting in the clothing market and a shift in mix towards lower margin categories. 

"Whilst overall performance in the quarter was impacted by challenging market conditions - particularly in clothing - the supermarket's core food business proved more stable," Asda said. 

Last month the other three of Britain's traditional big four retailers - industry leader Tesco, Sainsbury's and Morrisons - all reported subdued Christmas trading, highlighting a challenging trading environment. 

Industry data published earlier this month showed all of the big four continuing to lose market share to German-owned discounters Aldi and Lidl, who, unlike the big four, are opening lots of new stores.