Figures for the 12 weeks ending 15 September show Tesco sales down 5.6% on the same period last year, leading to a 1.9 percentage point drop in market share. Dunnes grew sales by 3.3% on the same ‘back to school’ period last year.

SuperValu’s strong summer performance continued with sales growth of 1.8%, improving its share to 19.7%. Aldi and Lidl continue to expand market share, with respective growth rates of 24.3% and 13.1%. Based on current growth rates, Aldi look set to overtake Lidl in the coming months.

David Berry of Kantar Worldpanel said: “The build-up to the key Christmas period will show if the discounters can sustain their strong growth or if a ceiling is starting to be reached. Their ongoing growth, combined with the improved performance from Dunnes, has placed pressure on Tesco. This decline also reflects the strong performance posted by Tesco last year and its record market share over the summer of 2012.”

Meanwhile, grocery inflation stands at 4.8% for the 12 week period ending 15 September 2013, down from the 5.5% seen last period.

The international Tesco plc yesterday reported underlying group pre-tax profits fell 8.4% to £1.47bn on a constant currency basis. Sales in Ireland in the second quarter were down 4.4% when new stores were excluded.