Tesco (TSCO) once more looked like the clear winner amongst the big four from this week’s grocery market share data, but the City had other ideas.

Tesco grew its market share to 28.3% amid a 1.6% sales boost in the 12 weeks to 4 December, according to Kantar Worldpanel, while Nielsen had Tesco’s 12-week sales growing by 1.7% compared to declines for all its big four rivals. But Tesco was one of the five worst-performing blue-chip stocks on the FTSE 100 on Tuesday, plunging 3.8% to 204.9p as the City focussed on the four-week data that appeared to show the supermarket’s sales dramatically slowing.

Tesco’s 12-week growth edged back from 2.2% to 1.6% according to Kantar, with its four-week sales dropping by 0.9% after 3.6% growth in the previous period. Tesco slipped to third place amongst the big four in the four-week snapshot, with Morrisons (MRW) up 0.2%, Sainsbury’s (SBRY) down 0.6% and Asda down 3.9%.

The City may have taken a dim view of Tesco’s data, but analysts were more sanguine. “Four week data is always very volatile [and] we expect this to reflect a temporary blip rather than change in direction for Tesco’s recovery,” said Bernstein’s Bruno Monteyne. HSBC’s Dave McCarthy commented: “Tesco once again won market share across the period, and while it was not immune to the November slowdown, it continues to be the momentum play running into Christmas.”

Nielsen found the wider grocery market saw sales value drop 0.4% and volumes slip 0.3%, but Kantar Worldpanel found grocery sales rising 0.7% amid an almost disappearance of long-standing deflation. Sainsbury’s and Morrisons and Morrisons shares rose 1.6% to 245.8p and 0.6% to 226.4p on Tuesday, supported by Kantar’s measure of deflation dropping to -0.1% from -0.5% in the previous period. The listed grocers were also supported by a continuing fall in discounter growth, with Kantar finding Aldi’s 12-week growth slipping to 10% and Lidl’s to just 5.7%.

“A drastic reduction in the German discounters’ sales growth had been the story of recent months,” noted Jefferies. “Consumers’ reduced propensity to trade up looks to be also confirmed by anaemic growth at quality operators,” the broker added, noting the slowdown at Marks & Spencer to 1.8% growth from 6% year-to-date.

Elsewhere this week, PZ Cussons (PZC) edged down 0.6% by Thursday lunchtime to 311.9p having dropped as low as 306p after it said its first half performance remained on track despite huge currency volatility in its key Nigerian market. “Across PZ Cussons’s trading world there are more challenges than not,” said Shore Capital. “Hence, it is pleasing to see the generally maintained market share positions by the group’s brands, positions sustained through high innovation rates.”