Tesco is winning the

online supermarket war

in the UK, although Sainsbury’s internet customers spend more per order and incur lower delivery charges, according to a new study.

Research group comScore Networks said Tesco.com captured two thirds of all online grocery orders in the first seven months of this year, generating sales of approximately £2.5 million per day. Its closest competitor was Asda online, which took 16%, followed by Sainsburystoyou.com with 14%.

Customers of Sainsbury’s, however, spent the most per order, averaging almost £90 compared to £80 for both Tesco and Asda. Asda and Sainsbury’s online shoppers also bought more items per order, with both averaging 69 units per order compared to Tesco’s 58.

The research, comScore said, was culled from the behaviour of more than 2 million consumers which had given the firm permission to monitor their online activities.

Having tracked the delivery costs charged by each retailer, it found that Sainsbury’s online customers incurred the lowest average delivery charge during the period, at just over £3. Tesco’s online customers paid over £4 per delivery, and Asda’s online customers paid the most at nearly £5.50.

Said Bob Ivins, managing director of comScore Europe: “Delivery charges represent a key component of overall online grocery service, because the top three sites each offer complex pricing structures based on the delivery slot chosen and the amount ordered.

Tesco.com was boosted by the purchase of more than 11 million bananas during the period; its top item by volume. Its Luxury Soft Toilet Tissue 12-packs were also a winner, generating almost £2 million over the year, more than any other product.

The best performing items at Tesco.com seem to be an interesting mix of fresh fruit and vegetables with a reasonable shelf life, like carrots, onions and apples, and large-volume containers that are awkward for consumers to carry home themselves,” said Ivins.

Tesco has a 31.5% share of the UK’s overall retail market. Its online sales reached almost £1 billion last year, compared with total group earnings of £38.3 billion.

Earlier this week, Paypal released a report which predicts that UK online groceries will make £6.25 billion in sales by 2010, an increase of 235% over their revenues last year.  

Meanwhile, Asda recently said it is set to launch its first affiliate marketing programme. It has teamed up with TradeDoubler to promote the entertainment, floral, contact lenses, gift and photography sections of its website.