The unofficial race between the UK's leading supermarkets to see who can save the most plastic bags stepped up a gear yesterday after Tesco claimed it has reduced the number of single use carrier bags distributed over the last two years by two billion.

The company said that since the launch in August 2006 of its scheme for offering customers points on their Tesco reward cards if they use their own bags monthly bag use has fallen by 40 per cent to 200m bags.

Lucy Neville-Rolfe, corporate and legal affairs director at Tesco, said that the rate at which customers were turning away from plastic bags was accelerating. "It took more than 14 months to save the first billion bags but the second billion was achieved in less than nine months, showing that the trend is rapidly gaining support," she said.

Tesco maintained that the figures were also evidence that its approach of incentivising people to reduce plastic bag use was working. In a thinly, veiled swipe at government plans for a possible tax on single use carrier bags, Neville-Rolfe said that the company had helped customers cut bag use by 40 per cent "without a bag tax adding to the cost of their weekly shop".

"Our customers have shown us how keen they are to break this environmentally-damaging habit of a lifetime," she said. "The "carrot" approach clearly works."

However, it is unclear if Tesco's analysis of the relative effectiveness of a bag tax stacks up. Last month, M &S announced that it had achieved an 80 per cent drop in the distribution of food carrier bags following the recent introduction of a five pence charge for the bags.