Asda has declared itself “Britain’s biggest poundshop” after notching up a 12th successive year as the cheapest supermarket in the Grocer 33 survey.

Despite fierce price-cutting campaigns and frenetic promotional activity from its rivals, Asda increased its lead to win the price award again in The Grocer’s annual mystery shopping competition.

A weekly shop this year cost on average £52.96, a tidy £1.34 less than at second-placed Morrisons. Last year, a shop at Morrisons cost just 98p more than at its bottom-slapping rival.

Asda chief merchandising officer Darren Blackhurst said the win was down to Asda’s everyday low costs and clear pricing strategy.

“Asda is the biggest pound shop in the UK,” he said. “We have over 7,000 products at £1 and the pound coin is highly visible through our stores. The magic of a pound is its simplicity. If customers see something that used to trade at, say £1.70 reduced to £1, it’s easy for them to know what they’re saving.”

Tesco came third, with an average basket of £54.80, Sainsbury’s was fourth at £55.87 and Waitrose, at £62.47, was a distant fifth.

But it was a different story for Asda on service and availability, the other two G33 pillars. Last year Asda won a historic treble but this time round came a distant fourth on both service and availability, ahead of only Tesco on both counts.

Morrisons scooped the awards for service and availability, though its victories were only secured in the final week of the 52-week competition. With a week to go, Morrisons and Waitrose both had 13 top store victories. But thanks to Kim McCutcheon, a checkout assistant at the Almondvale, Livingston store, Morrisons won.

Availability was a similar triumph. Sainsbury’s had risen from the bottom of the availability league table to sit at the top for almost every week of the year, albeit with fierce rivalry from Morrisons. But two out-of-stocks in Sainsbury’s Loughborough store last week were enough to let Morrisons nip past its rival at the finish to reclaim the availability award.

“We really focus on the service we offer our customers and when staff get it right, we praise them,” said Morrisons group retail director Mark Gunter.

Gunter was scathing about retailers that fail on availability: “Going into a supermarket with bad availability is like going into a pub with no beer.”

The three awards will be presented at The Grocer Golds on Wednesday at London’s Dorchester Hotel.  The final G33 award for store manager of the year will be revealed after a round of Dragons’ Den-style grilling on the day, along with 17 other gongs.