They are separated by the faintest of margins, but Asda has narrowly undercut Morrisons to record its fourth week as cheapest retailer.

Asda's £52.32 basket was just 9p less than Morrisons' total, although they did not match as many prices as usual. Last week, 18 items had the same price at Asda and Morrisons, but here they matched on 11 products as the battle on price comparisons intensified.

Five of the products on the list were cheapest at Asda, the most significant being the John Smith's beer which was 27p less than last week. Asda also beat Morrisons on the mango after the runner-up raised its price by 41p to £1.19, compared with 98p at Asda.

But this wasn't Morrisons' biggest hike. In a busy week for price changes, the second cheapest retailer added £2 to its sirloin steak to match Asda and Tesco's price and also 10p and 11p to the cauliflower and Hula Hoops to make each the priciest on the list.

However, its grapes were a list-beating £1 cheaper than its rivals and it dropped its cherry tomatoes by 18p to beat the competition. Morrisons' also had lowest prices for the organic milk and Ambrosia.

In the previous survey, Tesco was a sizeable £3.70 off Asda's total, but it was just 34p more this time.

A £1.50 cut to grapes helped it narrow the gap, as did a 49p reduction on sausage rolls, which gave them the cheapest price of £1.

But Tesco also ramped up its Hovis loaf by 56p to the second-highest price of £1.48 and its 69p cherry tomatoes were among six items which were pricier than the rest of the big four.

Ten of Sainsbury's prices were the most expensive of the big four retailers and it dropped back to third place with a £54.20 basket. Its single price hike was 16p on the Colmans mustard while its ongoing 99p Doritos offer undercut the rest of the big four by at least 42p.

Last week, Waitrose was a hefty £8.10 off fourth place but has now narrowed the gap to just £3.35. With a £57.55 basket, it offered the cheapest sirloin steak and Weetabix 41p lower than Asda's.

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