No wonder Justin King was looking so pleased with life at today’s 90-minute briefing in Holborn, attended by The Grocer’s newshounds.

Sainsbury’s this morning unveiled like-for-like growth (minus petrol) of 3.6% to emerge as a pretty clear winner in the Christmas period, which it said was its best festive season ever.

That rate of growth harks back to the golden age of 2008 and 2009, when all you had to do to rack up stellar numbers was put a spud on a stick and call it a premium potato lolly.

Yesterday this column noted that ‘quality’ was identified as the year's key battleground by many of the expert pundits in our 2011 preview. But the trading up has already begun. That’s certainly Verdict’s, er, verdict.

The data analysts today published new research showing that 8% of grocery shoppers – equating to more than three million people – traded up from their regular supermarket “to a more premium provider” for Christmas.

Admittedly, almost 5% traded down – less a sign of Scrooge-like tendencies than some defining their seasonal excess through quantity over quality.

But the shift is still significant. And while Verdict picked out Waitrose and M&S as the likely beneficiaries, yesterday’s data from Kantar will have made happy reading for Justin’s gang.

Quarterly market share figures showed Sainsbury’s was just 0.2 percentage points behind Asda in the final three months of the year, having slipped to third behind the Leeds-based chain in 2003. Over the crucial four weeks before Christmas, Sainsbury’s overtook it.

Part of that is surely the temporary trading up referred to by Verdict. And part of it is also indicative of Sainsbury’s general upward momentum.

“It has never been an objective of the business,” King twinkled at today’s briefing with regards to overtaking Asda. “It’s only natural that if you deliver better growth than your competitors you're going to overtake them or catch them up.”

True enough. But Kantar’s next batch of quarterly data promises to be even more revealing.

More slices of Daily Bread