The price of Kingsmill bread is lagging 20p behind arch-rival Hovis, analysis in The Grocer 33 has revealed - stumping industry commentators who suggested that the prices of commodity-based products were increasing across the board.

This week new figures revealed the fastest rise in the cost of food since 1993, up 6% year-on-year. The rising price of key commodities such as wheat, milk, cocoa and fats was blamed. Analyst Andrew Saunders at Panmure Gordon told The Daily Telegraph: "I've never seen food inflation like it. All the manufacturing cost increases [are] being offloaded straight to retailers, who in turn are passing it immediately on to the consumer."

But our analysis revealed that while food price inflation continues - with dairy lines soaring again this week across all multiples - the price gap between the three leading bread brands, Kingsmill, Warburtons and Hovis, was widening. In the past five weeks, the average cost of Kingsmill 800g white fell: from 99p to 93p.

Meanwhile Warburtons 800g white has stayed about £1, on average and is currently £1.01. The costliest loaf was Hovis, which rose from £1.04 to £1.13 in the same period.

Industry experts said the gap was "bizarre" given the rise in wheat prices since the summer. The cost of a tonne of bread wheat has risen from £65 in August 2006 to £130/tonne in June and was trading at £205 as The Grocer went to press.

In a statement this week Premier Foods said successful negotiations to increase the price of Hovis by 7.5% last week were welcome and had helped lift group sales 3%. It blamed retailers' delay in increasing the price of Warburtons and Kingsmill loaves for lower sales volumes for Hovis. "Combined with higher wheat prices, this had led to trading profits for the division being significantly lower."

Gordon Polson, director of the Federation of Bakers said he was flummoxed: "I don't understand. All bakers are suffering the same price increases and you would expect that reflected on shelf. Kingsmill's low prices are bizarre."

A BRC spokesman suggested Kingsmill, which has declined to comment, may be paying a different price for wheat, having bought stocks in advance, or ABF was absorbing cost increases, keeping prices low as a means of gaining market share. Analyst Simon Peacock warned Kingsmill's cheap prices could have damage the brand. "I'd be surprised if retailers were absorbing the costs. Kingsmill may have said it needs a lower price to shift volume. But this makes it a loss leader ."

The wide variations in bread prices were not reflected in dairy. On top of the 11.3% rise in the cost of milk, cheese and eggs recorded by National Statistics in the past year, The Grocer 33 saw across-the-board rises in cream (up 17%), and butter (up 25%). As for cheese, Asda increased its own label Cheddar by 8.5% and Morrisons Cheddar rose 43% to £5.44.

Also successful in negotiating price rises across its ranges was Northern Foods. In the week the Goodfellas pizza reported first-half pretax profit up 38%, boosted by a ready meals contract with M&S, group chief executive Stefan Barden said retailers had accepted the price pressures the supplier faced from wheat, cocoa and fat costs.