Morrisons appears to have lost substantial market share to its rivals over the past month after the sales gap between it and that of Tesco, Asda and Sainsbury's widened, according to industry data.

Kantar Worldpanel revealed that Sainsbury's was the grocery sector's top dog, posting a market-busting 6.1 per cent rise in sales over the four weeks to 2 September, which included the second week of the Olympics. The market research firm also expects Sainsbury's to have benefited from its sponsorship of the Paralympics that ended on Sunday.

Morrisons delivered a lacklustre 0.5 per cent rise in revenues over the four weeks, compared with till-roll growth of 2.6 per cent across the sector. It lagged Asda's 4.7 per cent and Tesco's 2.6 per cent, as well as Aldi's phenomenal 28.8 per cent and Waitrose's 10.3 per cent growth.

Edward Garner, a director at Kantar, suggested that sales at Morrisons were weaker because it does not have an online grocery offer and only has a small number of convenience stores, as these are the "two areas which are currently major contributors to the growth of its three main competitors".

Morrisons' investors will be reassured by the fact that convenience and internet retailing are less profitable than large store operations.

Tesco's market share slipped by 0.1 per cent to 30.8, Kantar reported. Dave McCarthy, an analyst at Investec, said: "Tesco must be disappointed. It has lost share and sales growth has lagged the industry average... despite a huge investment in new stores."