It's been all change for The Grocer 33 over the past six months. We have increased the frequency of basket rotations from once a month to once a week, and boosted our pool of products from which our shopping list is constructed, giving us a much broader insight into the pricing strategies within the major multiples.

However, there is one element that has remained constant: Asda's dominance of the pricing tables. Our latest findings reveal the retailer has once again retained a firm grasp on its crown as The Grocer 33's cheapest retailer, having claimed the cheapest 33-item shopping basket for 70% of the time, or 18 of the past 26 weeks.

Tesco was second in terms of price. But with just five cheapest shopping baskets to its name over the past six months, it remains a long way behind its rival. This is supported by data from The Grocer 100 (see facing page).

The results also show that the competition to be named the nation's third-cheapest supermarket has never been so fierce.

Morrisons and Sainsbury's remain locked in a furious battle to claim the bronze and while Morrisons has claimed the cheapest shopping basket twice since our End of Year Report on June 10, our findings reveal that when compared with each other, Morrisons has been cheaper than Sainsbury's for 13 of the past 26 weeks and Sainsbury's for the remaining 13.

However, while price is clearly a burning concern for the top four, further exclusive data from The Grocer 33 shows that the equally weighty issue of availability has slipped off the boil.

Availability levels have plummeted, with The Grocer 33's mystery shoppers reporting a sharp rise in the volume of out of stocks.

Somerfield posted the weakest performance in terms of availability. The retailer chalked up 48 out of stocks in the last 26 shops conducted. That's 22 more than in the previous six-month period. Meanwhile Sainsbury's, which has implemented a number of initiatives to boost availability over the past year, was not far behind with 30 out of stocks - virtually double the number we recorded six months before. And Waitrose which was voted the best retailer for availability in The Grocer 33's end-of-year review, totted up 25 out of stocks, 16 more than previously, earning it an availability score of 97.11%.

Tesco had 23 out of stocks compared with 16 in the previous period, lowering its availability score to 97.26% while Asda, which is in second place with a score of 97.75%, had 19, two more than previously.

Morrisons put in the best performance in terms of availability. It is the only retailer to have not incurred any out of stocks for the past three weeks (up to 9 December), but even its score of 97.85% was well below what it had achieved six months ago.

However, while availability may appear weakened, Morrisons has proved it is still king of the customer service castle, with nine Top Store Awards to its name over the past six months, pulling ahead of nearest rival Sainsbury's, which had six.

As well as availability, The Top Store Award winners are judged on a variety of service-based factors such as staff responsiveness, store cleanliness, layout, signage, and service at the checkout, time spent queuing (a particularly contentious issue with shoppers) and whether or not their bags were packed for them.

Shoppers at Somerfield spend the least amount of time at checkout, just four minutes and 23 seconds on average, while shoppers at Tesco, which has introduced cutting-edge infrared technology to speed up queuing times, spend the most - six minutes and five seconds on average.

Waitrose, Asda and Somerfield were neck and neck in terms of Top Store Award wins in the six-month period with three, while Tesco claimed the award twice.