Supermarkets are accused of failing to adequately stock shelves

There are so many gaps in availability that undercover investigators, visiting a different Tesco branch every week for a year, got a full basket just three times.

Waitrose was no better, Asda only marginally so, and even the best of the five major chains, Morrisons, could only offer every item on a list six times in 12 months.

The problem is getting worse according to the annual Grocer 33 table, an influential round-up of a full year of mystery shoppers testing supermarkets.

The Grocer magazine sends investigators to a different branch of Asda, Morrisons, Sainsbury’s, Tesco and Waitrose every week with a list of 33 everyday items to buy.

As well as monitoring the price and service, it also looks at the availability of items, which include the kind of things every shopper buys like tea, bread and milk.

In the past 12 months, out of 250 visits, the list could only be completed 21 times, which works out at 8 per cent.

Morrisons was best with six full baskets, Sainsbury’s provided five, Asda four and both Tesco and Waitrose just three.

There were 53 baskets - more than one in five - returned with three or more items missing, with Tesco the worst culprit, having been the best the year before.

In the previous 12-month period, there were 38 full baskets, and all but Morrisons managed double figures for the number of times they returned all 33 items.

Analysts blamed the problem of increasing breakdowns between the supermarkets and their supply chain and underestimating customer demand for promotions. Suppliers are not keeping as much stock during the economic recession to avoid the costs of wastage if they do not sell everything.

This also means that they have less to supply the supermarket chains when several of them order the same thing at once unexpectedly – possibly one chain runs a promotion and others decide to copy.

There is also a problem with different branches having different needs when such a promotion is run, said The Grocer.

A chain may order an extra 100 units of one product for each of its branches when running a promotion like a “buy one, get one free” deal.

But while one branch could sell out within a day, another could be left with unsold stock for a couple of months, said the publication

Alan Braithwaite of supply chain consultants LCP said: “Promotions lead to massive volatility in demand. The spike could be fivefold in one store and 25-fold in another.”

The Grocer’s editor Adam Leyland said: “Five years of intensifying promotion-based price wars, combined with an increasing disconnect between supermarket and supplier planning, and just-in-time stock inventories, have resulted in major shelf gaps amid ever-more erratic sales.”

Yet despite the lack of full baskets, supermarkets can point to The Grocer’s figures showing an average 95 per cent of the 33 items are available at any one time.

Sainsbury’s said its own figures showed it had improved over five years, adding: “We performed well against our targets.”