The supermarket sector is in decline for the first time in at least 20 years after figures today showed sales were 0.2pc lower over the last 12 weeks.

The latest till-roll figures from Kantar Worldpanel highlight the impact of price cutting brought on by the rise of discounters such as Aldi and Lidl.

It is the first time since Kantar records began in 1994 that the British grocery market has gone into decline, with the average basket of everyday goods such as milk, bread and vegetables now costing 0.4pc less than one year ago.

The big four chains all suffered falls, with Asda faring the best as sales in the 12 weeks to November 9 fell 0.2pc, with its market share holding firm at 17.2pc.

Fraser McKevitt, head of retail and consumer insight at Kantar Worldpanel, said: 'The declining grocery market will be of concern to retailers as they gear up for the key Christmas trading season.

'This is bad news for retailers, but good news for shoppers, with price deflation forecast to continue well into 2015.'

Asda, which posted its worst quarterly sales performance in nearly a decade last week, has accused its major rivals of panicking through a range of costly promotional measures such as the giveaway of vouchers.

Tesco, which is being investigated by the Serious Fraud Office over an accounting scandal, saw its sales fall 3.7pc, although this is a slower decline than recently. Its market share fell to 28.7pc from 29.8pc a year ago.

Sainsbury's, which launched £150 million of price cuts last week and said it would make cost savings of £500 million over the next three years, said sales fell 2.5pc. Its market share fell to 16.4pc from 16.8pc.

Morrisons also suffered, seeing its sales fall 3.3pc and its market share slip to 11.1pc from 11.5pc.

The discount supermarkets continued to make gains at the expense of the major players, with Aldi's sales 25.5pc higher than a year ago and its market share up to a record 4.9pc.

Lidl also performed strongly, seeing its sales jump 16.8pc and taking its market share up to 3.5pc.

At the top end of the market, Waitrose saw its sales grow 5.6pc, boosting its market share to 5.1pc.