For the 12th consecutive period, Tesco has grown more than two per cent, marking the first time the retailer has achieved that since March 2011, and underlining the supermarket's progress under Dave Lewis. Its overall market share stood at 27.6 per cent for the 12 weeks to 22 April 2018.
Sainsbury's has a 15.9 per cent market share, while Asda has 15.5 per cent of the market, according to the latest figures, with Sainsbury's sales edging up 0.2 per cent over the past 12 weeks, while Asda's rose by 1.4 per cent.
Both had dropped market share compared to this time last year though, down 0.3 percentage points and 0.1 percentage points respectively. Overall, the British grocery market grew at its slowest rate since March last year at two per cent due to lower grocery prices.
Asda outsells Sainsbury's in branded goods and also attracts a greater number of households through its doors, according to Kantar Worldpanel.
A tie-up would also provide the advantage of the different customer bases, with McKevitt noting Sainsbury's registers nearly 59 per cent of its sales in London and the South East, while Asda racks up nearly two-thirds of its sales outside of those two areas.
Morrisons was crowned the fastest-growing traditional supermarket over the period, with sales growth of 2.2 per cent and holding market share at 10.5 per cent, and it is winning over Londoners - growing at its fastest rate in the capital.
Fraser McKevitt, head of retail and consumer insight at Kantar Worldpanel, said:
This is a pivotal moment for the British grocery market. A merger between Sainsbury’s and Asda would transform the traditional landscape placing nearly a third of market share in the hands of the joint supermarket giant, though the march of the discounters – and any enforced store closures – could impact this figure.
Lidl was the fastest-growing name on the list, with sales up 9.1 per cent and a 5.4 per cent market share - up 0.4 percentage points from this time last year, while Aldi racked up 7.7 per cent growth with a market share edging up by 0.4 percentage points to 7.3 per cent.