ON Sauchiehall Street on a bitter winter day in Glasgow, workmen are hurrying to get the new Tesco Metro finished in time for the (probably not very) grand opening next Monday.

For years this was home to Littlewoods, but since the start of the recession it has mostly lain empty.

One workman stands to one side, frowning from beneath his yellow safety helmet as the busker's strains of Don't Look Back In Anger fill the surrounding street.

"Dunno why they need another one," he suddenly grumbles, unprompted. "You've already got that one over there," he nods at the Sainsbury's Local.

"And there's the new Co-op down there," points a shopkeeper with a cigarette. "And there's another Tesco just over there at Charing Cross."

As anyone walking with their head up over the past couple of years will have noticed, these small supermarkets have been springing up like toadstools. Admittedly Tesco is more focused on opening small-scale Express stores than medium-sized Metros like this new one, but the principle is the same. The retail giant that led the way out of the high street to out-of-town hangars between the 1980s and 2000s is returning whence it came.

Since the start of the economic crisis Tesco has roughly doubled the pace at which it opens these outlets, unveiling 142 new Express stores in 2011-12 for example, around 10% of them in Scotland. It opened its 1500th Express last year and plans for another 200 for 2013.

At the same time it will add another 100 outlets to its 800-strong chain of One Stop convenience stores. Tesco might be telling us that Every Little Helps, but Every Little Supermarket Helps is a more fitting motto.

Once again, the move is being mimicked by the competition. The number of Sainsbury's Locals has near doubled in five years to approaching 500. One of the priority regions is Scotland, where there are 38: eight new ones will open during the year. Standalone M&S Simply Food boasts comparable numbers, focusing as much on petrol stations and motorway services as affluent high streets.

And if that does not sound like enough mini-mes, let us not forget Asda, with 150 small outlets from its purchase of Netto a couple of years back. Similar in size to a Lidl or Tesco Metro, analysts suspect expansion plans are imminent. Morrisons has also been trialling a handful of small stores branded M-local. Last week it was linked with 20 of HMV's outlets (if Tesco or Sainsbury don't get there first).

This Panzerish assault on local centres does not seem to attract much opposition from the authorities. The Government has impressed anti-supermarket campaigners recently by appointing an adjudicator to help tackle the multiples' abuse of suppliers, but seems unwilling to do anything about this issue.

As Shane Brennan, public affairs director of the Association of Convenience Stores (ACS) says: "We have tried at Westminster and Holyrood, but they don't really engage with the long-term argument. There are strong supporters of supermarkets out there that see them as incredibly positive."

David Kaye, a retail lawyer at Harper Macleod in Glasgow, explains that if a commercial property already has permission for retail activities, there is very little a council can do to stop a supermarket from moving in. In many cases, faced with high numbers of empty units, they appear to welcome them with open arms.

"They need retailers to open up in town centres," he says. "If you have got a recognised brand that's really good covenant for the owner. Why would you fight against that? Planners have appeared to be quite lax in this respect.

"And thank goodness for that," he adds. "Yes, they'll put a squeeze on local guys, but that's always been the way of it. When they open up in a big out-of town store, that's a much bigger threat to small retailers' independence."

The supermarkets might not quite put it that way, but they certainly argue that their small stores encourage shoppers to tread high streets and visit other shops at the same time. They also play up job growth, pointing out for example that the new Glasgow Metro is creating 118 jobs, for which there were over 2500 applicants. Others would counter that this wave of openings threatens wall-to-wall homogeny in the very areas where the smaller independents have continued to survive.

The backdrop is of course that many small retailers have been struggling to keep their heads above water since the bottom fell out of consumer demand five years ago. Scottish retail's December performance was 1.5% sales growth year on year, a decline once you account for inflation. It is a sign of the times that that was heralded as a decent result compared to the horrors of the autumn.

"There's a real space-race going on between the multiples to open as many stores as quickly as possible," says Brennan. "Lots of independent retailers in our sector are seeing the big players opening up around the corner and they are really worried about it.

"It can take sales down maybe a fifth or even a quarter for them. That can make some businesses close."

One curious thing from the multiples' point of view is that the results are highly questionable. They too have been hurt by the reluctant consumer, who is spending less per visit and more inclined to trade down to Lidl, Aldi and the pound stores.

According to a recent report by Investec, overall unit sales in supermarkets were down by about 5% both in 2011 and 2012. Not only is this expected to continue, it is actually being exacerbated by the smaller supermarkets.

THE multiples began this strategy around a decade ago for several reasons. They needed to find a new way to grow once the number of big stores was approaching saturation point and they discerned a change in how consumers wanted to shop. The vogue for a big weekly splurge out of town started to be replaced by a preference for numerous trips to local stores.

This trend received impetus as driving became less appealing owing to rising petrol prices and static wages. Studies showed people were beginning to avoid big supermarkets because they knew the retailers' genius for promotion tempted them to spend much more than intended and were increasingly preferring small stores even though the prices were a few percentage points higher.

The aggressive opening of smaller stores has been used to offset falling sales at the big stores. The problem is that the more small stores you open, the more the sales fall at the big ones, and the small stores are considerably less profitable in spite of the higher prices.

McCarthy of Investec says: "You have higher delivery costs, you have to use a smaller van because you can't get a big articulated lorry down a village high street, you have more labour intensity.

"The shelves are small so you have to keep restocking them. The range is small, so you can't put many of your higher-margin goods there – 70% of your space has to be taken up with staples like bread, milk and tea."

According to McCarthy's report, the difference in margins can be 4% or 5% against 12% to 14%. Every extra unit of sales the multiples get from a small store rather than a big store moves their total profit margin towards this lower level. Yet they are driven to keep doing it because it is what customers want, and because they risk losing more by not opening more small stores if competitors keep opening them. It leads to the kind of competitive pile-up happening on Sauchiehall Street.

McCarthy does not think there is enough consumer demand to satisfy all these extra stores, and that the result could be as disastrous for the weaker chains as it could be for small businesses.

"It's rational for each individual retailer to carry on opening space, but the cumulative outcome is irrational. You end up with more stores, more space, more capital in an industry that's got no volume growth," he says.

Brennan of the ACS says that the openings have become increasingly more indiscriminate as the pressure to dominate an area has mounted. "The supermarkets' threshold for deciding whether a property is viable or not has come down," he says. "They are pricing out the small players."

And so it continues. Once the buzz of construction ends at Sauchiehall Street next Monday, the programme could well be shifting to another site of winners and losers around the corner from you.