More than £11m of spending was switched from Sainsbury’s to its competitors in the 12 weeks to November, according to TNS Worldpanel data leaked to The Times.

In the period, Sainsbury’s gained a net £700,000 from Asda and smaller gains from Netto and Farm Foods.

However, around £2m of spending was switched to Tesco, £4m was switched to Waitrose and a further £2.5m went to Aldi. The figures suggest Tesco’s introduction of double points on its Clubcard has lured customers away from Sainsbury’s, and Waitrose’s sales have grown since it introduced a value range in March.

Many analysts have warned that Sainsbury’s faces an uphill battle now that Tesco has regained its form. Tesco is also planning for an intense price war this Christmas, alongside its rival Asda.

A Sainsbury’s spokesman told The Times: “We continue to grow market share and we are now serving over 18.5 million customers each week, up 800,000 on this time last year. We also have an excellent growth opportunity through our expansion plans.”

Sainsbury’s has confounded critics in the recession by reporting strong growth as many said its upmarket position would mean it would suffer.

The TNS data also reported that Tesco’s drive to become Britain’s biggest discounter has succeeded, as it has taken £7m of spending from Aldi. It did however lose customers to Waitrose and Morrisons.

Separately, Tesco has told City analysts that it wants to double the size of its convenience store empire. It has around 1,000 Tesco Express shops and believes there is potential for 2,000. Both Sainsbury’s and Waitrose are also gunning for new convenience shops.

Tesco, which this week is showing analysts around its banking operation in Scotland, is poised to reiterate the prospects from its push into banking in spite of a slowdown in the launch of a network of bank branches in its stores.

The retailer indicated it would open 30 branches in stores this year but has so far only opened six. The retailer is thought to be waiting until it offers a wider range of products, such as current accounts.