By Jonathan Davies

Sainsbury's has become the UK's second biggest supermarket after overtaking Asda's market share.

It comes after Asda's sales fell much quicker than any of its rivals. The Walmart-owned supermarket reported a 2.7% drop in sales for the 12 weeks to 19 July, according to market researcher Kantar Worldpanel.

That fall, stronger than any of the 'Big Four' and the likes of Co-Op, Iceland, Aldi and Lidl, took Asda's market share down 0.6 points to 16.4%.

Sainsbury's sales also fell, but by just 0.3% meaning it lost 0.1 percentage points off its total, leaving it with a share of 16.5%.

It is the first time since 2003 that Sainsbury's has had a bigger market share than Asda, outside of Christmas periods. Sainsbury's has often overtaking its rival during Christmas trading over the past decade.

“Asda has had a slow 2015,” said Fraser McKevitt from Kantar Worldpanel. “Asda is being run more for profit rather than market share or revenue. It also hasn’t got a substantial convenience store estate while convenience is acting as a real growth driver for Sainsbury’s.”

Elsewhere, Tesco's market share fell 0.4 percentage points to 28.5% and Co-Op reported its first rise in sales in more than a year.

“The Co-op has been spending a lot of money on its estate and that seems to be having a benefit. It is getting younger, more upmarket shoppers,” said McKevitt. “This could be the start of life getting better for the Co-op.”