Welcome to what looks set to be another turbulent year for grocery prices at the top six supermarkets.

A number of significant changes have already taken place since our last report on 16 December, with the price of loose apples tumbling by 21p at Asda and Sainsbury's.

Meanwhile, as predicted in our previous issue, the big four are battling it out in a parsnip price war, with the cost of the roast dinner staples plunging by 40p at Asda to £1.48, in line with the price drop already posted by Tesco, while Morrisons has maintained its rock-bottom price of £1.09 per kg.

Bread prices are also set to rise in the new year as the cost of wheat continues its upward march (see page 12).

Morrisons has stepped up its promotional activity in this first week of January. This week's mystery shopper spotted 10 deals on 33 of the items on our list, not to mention the hoards of others around the store.

Morrisons also provided the cheapest overall shopping basket in this week's report - a sign, possibly, of things to come in the next 12 months as it continues to hone its competitive edge.

The retailer was matching Asda for price on 24 of the products on this week's list, six more than the same time last year, and was also cheaper than Asda for three items: parsnips, own label Brie, and a tub of own label houmous.

At £44.20 Asda, which had been once again crowned as The Grocer 33's overall cheapest retailer in the section's December six-month review, claimed the second-cheapest shopping basket.

Sainsbury's was close behind at £44.82, as a result of a more expensive price for loose oranges.

Meanwhile, some slightly more elevated price points on loose apples, closed cap mushrooms, and loose oranges caused Tesco to slip down to fourth position on the pricing tables with a basket worth £45.11.

At £51.66 Waitrose was the week's fifth-cheapest retailer, while Somerfield was £1.70 more expensive, thanks to the higher price of its own-label Brie.