If there is one clear sign that shoppers are feeling the pinch, it is the sight of mothers walking the aisles with calculators in hand.

Despite the surprisingly healthy retail figures last week, an Asda executive saw exactly this on a recent walkabout in one of the chain's heartland stores.

At the checkouts, women were emptying their trolleys in batches, with weekly essentials - bread, milk and nappies - loaded on to the conveyer belt ahead of items that could be offloaded if the purse ran empty.

The Asda executive's grim observations have not yet been reflected in official figures. According to the Office of National Statistics, retail sales volumes rose 1 per cent between January and February, confounding expectations of a 0.2 per cent fall. The survey suggests tighter credit conditions and a slowing economy have not yet prompted consumers to slash spending.

But the anecdotal evidence points to a changing landscape. John Lewis, a stellar performer in the past year, said recently that sales in its home division had moved decisively into negative territory in February and warned of challenging times ahead. Next, Argos, Wm Morrison and Debenhams have repeated the message.

Meanwhile, Borders Group, the US-based books retailer, became the first prominent retail victim of the global credit crisis when it announced on Thursday it had turned to its biggest shareholder for additional money and hired two investment banks to advise on a possible sale.

So just how bad could it get for retailers? According to Richard McKenzie, retail consultant at OC&C, a consultancy that has produced a report on the subject, some are likely to go under. "There will be a shake-out," he says. "It is a time when you get winners and losers."

Using evidence of spending patterns from the past two decades, OC&C has looked at the effect of a 1 per cent downturn in consumer expenditure and found that some sectors will be much harder hit than others.

Cyclical sectors such as DIY, electricals and furniture are likely to see a 1.5 per cent to 2 per cent fall in underlying growth with essentials such as food seeing a shallower dip in sales. Here, growth will slow to an estimated 0.6 per cent. "I was surprised DIY and gardening fell at three times the rate of food and grocery sales on average," says Mr McKenzie.

The stronger players have been able to consolidate their position in a downturn, including - on past evidence - the supermarkets, B&Q, Selfridges and Majestic Wine. But the mid-market players, already suffering strong competition as supermarkets encroach into their territory, are likely to suffer.

"A downturn shakes out the retail market with strong players emerging even stronger as weak players lose disproportionate share and, at the margins, collapse," the report says.

But OC&C concedes past downturns may prove an imperfect guide, given the structural changes taking place in the market.

The first is the huge expansion of clothing retailers' floor space, driven by volume-based chains such as Primark and New Look. If shoppers are already over-served, a downturn in consumer spending could hit clothes shops hard. "I do suspect that cases [of underperformance] will be much starker this time around," says Mr McKenzie.

The second is the dramatic rise in food prices. Global de-mand for biofuels and food staples is pushing up prices on every item in the shopping basket. This could make it even more volatile for retailers selling discretionary goods - while further shoring up the supermarkets.

Mysupermarket.co.uk, which tracks prices across the biggest supermarkets, says the price of a staple food basket of 24 items has risen on average by 11 per cent a week or £572 a year. For mothers on a budget, that is enough to make them concentrate on the pennies as well as the pounds.

Copyright The Financial Times Limited 2008