Much of Asda's lead was due to a price drop on Imperial Leather. Asda offered the product at the deep discount price of £0.75 - its lowest price in the past year - while the competition retained the price at or above £1.28.
Otherwise, much of Asda's lead was driven by everyday low prices, as it only had promotions on three of the items on this week's shopping list. One key example was Heinz Tomato Ketchup which Asda had available for £1.23, or 11% cheaper than the majority of its competitors.
Tesco's second-place showing was an improvement from the past few weeks when it surprisingly dropped to a mid-table position in our price survey. Our shopper at Tesco observed a few promotions, including a half-price offer on McCain Smiles, which were sold out by the time she arrived.
Morrisons, which has been cutting prices to regain market share, dropped to third place this week with a basket price of £36.62.
Sainsbury's dropped one spot to fourth place this week, as Tesco surged back into second place. Sainsbury's basket of goods cost £36.88 this week, or 4% more than price leader Asda.
Somerfield was fifth with a basket price of £40.70. Our national price survey showed that Somerfield had a £1.28 price for Imperial Leather, but our mystery shopper found an unusual local promotional offer of six for the price of four.
Waitrose was the most expensive supermarket this week at £43.31, a 22% premium over Asda. Waitrose's expensive kippers and own label Brussels pâté accounted for the majority of that gap, with the rest spread over a variety of items.
Our mystery shopper at Waitrose noted a high level of promotional activity, with offers on one fifth of the items on her shopping list, such as a bogof on McCain Smiles.