It said M&S's sales rose 12.3% in the 12 weeks to Jan. 29 year-on-year, giving it a UK grocery market share of 3.6%, up 0.4 percentage points on the year.

Last month, M&S nudged up its profit outlook after it reported a strong Christmas, and hopes are rising its latest attempt at a turnaround could succeed after decades of false dawns.

NielsenIQ's data showed market leader Tesco was the best performer of Britain's so-called Big Four grocers.

Its 0.3% sales decline significantly outperformed Sainsbury's, Asda and Morrisons, which had falls of 3.7%, 4.3% and 6.9% respectively.

The data echoed figures from rival market researcher Kantar published last week. However, Kantar does not include M&S in its monthly reports.

M&S also had weaker comparative sales numbers than the big four in the same period of 2020-21.

NielsenIQ said overall UK supermarket sales fell 2.9% over the four weeks to Jan. 29.

Comparatives were very tough, as in the same period last year the United Kingdom was in COVID-19 lockdown and sales grew 10.6%.

(Reporting by James Davey; Editing by Mark Potter)