The UK's biggest supermarket chain, Tesco, has reported a worse-than-expected drop in sales in the run-up to Christmas.

Chief executive Philip Clarke told the Today programme that customers were spending less but he admitted Tesco could have done more.

"We did underperform against our own expectations and the market we invested to be sure our prices were very competitive," he said.

"We deflated our prices. Our price inflation's half that of the market. But I've got to acknowledge we backed off some of our promotional and couponing activity too early.

"We've got to look to ourselves to make improvements."

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