Soaring commodity prices have caused grocery prices to leap 2.2% during the past six months, although the big four have battled to keep prices low. Latest data from The Grocer 100 reveals the average cost of our secret 100-item basket has risen £4.21 since our end of year review in June and now costs £190.74.

With an average trolley price of £175.72, Asda remains the UK's cheapest retailer despite being locked in a pricing tussle with Tesco at the start of the summer.

The turning point came in June when Asda's averages dropped to a low of £171.69, while Tesco's rocketed nearly 3% to £177.96. From this point, Asda's weekly average trolley hovered between £172 and £176 - well below other retailers.

Tesco challenged Asda in the first week of November and came within 5p of undercutting Asda's £174.37 trolley, but since then the gap has only widened with Tesco finishing the year at £182.39.

Morrisons and Tesco have been battling for second position in our weekly surveys, but comparing the core 100 prices per week, Tesco appears to have been the cheaper retailer.

The gulf between Tesco and Morrisons was most notable in mid-November when Morrisons' trolley was more than £10 more expensive than Tesco's £175.68 total.

However, in the past few weeks Morrisons' prices have been falling as Tesco's have been rising and this week Morrisons undercut Tesco by 63p with a £181.76 total.

Despite operating below the average, Sainsbury's prices started rising in September and have since remained between £185 and £189 - about 3% higher than its rivals.

The average price of a trolley of goods across the six retailers has risen most notably as a result of higher prices at Somerfield and Waitrose.

Somerfield finished June as the priciest, despite its trolley being about £2.50 less than Waitrose in late July and August when Waitrose's prices were static. But since October, little has separated the two and their premium prices have increased the average cost of a trolley of goods.

Waitrose has pulled away from Somerfield, which had a £207.57 average, in the past few weeks and it finishes the year as the most expensive retailer with an average total of £208.88.