Aldi supermarket
A customer leaves an Aldi supermarketReuters

Discount grocery chain Aldi has overtaken Waitrose and is now the sixth biggest supermarket by market share.

Aldi had a 5.3% share of the overall grocery market in the UK in the 12 weeks to March 29. Waitrose in the same period had a 5.1% share of the overall market, leaving it in seventh place in terms of sales.

Aldi plans to capitalise on its success by almost doubling the number of its UK stores from 531 to 1,000 by 2021.

Fellow German supermarket Lidl recorded sales growth of 12.1%, taking its market share to 3.7%.

Sainsbury's grew sales by 0.2% and Tesco by 0.3%, while Asda and Morrisons declined by 1.1% and 0.7% respectively.

Tesco, Asda, Sainsbury's and Morrisons all saw their market share fall, although Sainsbury's and Tesco both slowed the rate of their decline.

The research, carried out by Kantar Worldpanel, showed the discount grocery stores Aldi and Lidl have become much popular in recent years and put increasing pressure on the UK's big four supermarkets; Tesco, Asda, Sainsbury's and Morrisons.

"Firstly, the so-called discounters Aldi and Lidl now command a combined 9% share of the market. In 2012, the same two retailers only accounted for 5.4% of grocery sales," said Worldpanel's Fraser McKevitt.

"Secondly, the 72.8% share taken by the biggest four retailers is now at the lowest level in a decade," he said.

Across the sector, consumers are continuing to benefit from falling prices linked to low inflation and a bitter price war.

Low prices at Aldi and Lidl and changing consumer shopping habits have led to major supermarkets slashing prices in a bid to stay competitive.

According to Kantar, as a result, groceries are now 2% cheaper than they were a year ago.

Clive Black, analyst at Shore Capital, said the latest statistics were indicative of the "changing nature of grocery shopping patterns in the UK."

Looking ahead, Black added: "The industry should benefit from an improving British consumer scene in rising real incomes, and potentially improving mix and volumes. Against these encouraging processes are deflation, which looks likely to be with the industry for much of the year, and the competitive intensity of grocers seeking to regain lost ground to the discounters through investment."