Aldi is steaming ahead. So which of its rivals have been left behind?

The grocer has just announced a 15 per cent surge in December sales

Aldi lights up the grocery sector

This is how a well-paid City analyst explained to me why he shopped at Aldi: “It’s simple. Why should I put money in the pockets of Tesco shareholders?”

That an increasing number of people are sharing that sentiment can be seen in the 15 per cent rise in December sales the German retailer has just reported.

Combine a formidable reputation for value with a hard-won reputation for quality, one that stacks up very well when combined to the mainstream supermarkets (and is better than some), and you have a winning formula.

Pretty much the only reason to shun the place is snobbery. More fool those willing to put money into the pockets of Tesco shareholders for that reason. Or Sainsbury’s shareholders, for that matter.

That their numbers are shrinking, however, can be seen in Aldi stocking premium ranges designed to attract people with the disposable income to trade up. Not to mention the ski clothes it features in the aisle of mad decisions, where special offers live, ranging from clothes to consumer electronics to DIY to vacuum cleaners.

It is true that the 15 per cent sales rise over Christmas needs a bit of context adding to it. Aldi is one of those retailers that refuses to provide like for like sales figures. For those unaccustomed to City jargon, that means figures just from stores open at least a year. These would provide a picture of how the business is doing excluding the contribution from new store openings.

Aldi is opening a lot of new stores, and will continue to do so over the next few years. These account for a significant proportion of its growth, and it's hard to tell how much the exiting estate is contributing to its numbers. Enough to keep its bosses happy, is probably the answer.

Retail types keep saying that Aldi (and its rival Lidl) will eventually slow down and find a level when compared to the other grocers, as has happened with the other markets they have entered. It doesn’t look as if that’s going to happen soon in the UK market.

Aldi’s domestic competitors are more or less learning to live with the new reality because they don't have much choice.

But they’re not living well. The next couple of weeks will give an indication of how not well. With rumours of a Tesco revival doing the rounds of planet retail, and Morrison’s seeming to have turned itself around, Asda is looking very exposed (as is Sainsbury’s).

Retail analyst Nick Bubb this morning pointed out that the widely followed Grocer “33” weekly supermarket pricing survey in Saturday’s Grocer magazine saw Morrison’s win, even though the survey was done on Dec 17th, well before its latest price cuts. Its basket of £59.51 was 62p cheaper than Sainsbury and 92p cheaper than Asda.

This, he said, meant that Asda had to dole out a chunky £6.53 voucher because it wasn’t able to live up to its guarantee of being 10 per cent cheaper than its rival.

PS Amazon's just getting started.

Ouch. If things don’t start firing at Asda soon, one would imagine that its owner Wal-Mart is going to start... well, you can probably guess.