Superstore shifts its focus on to fresh food and health and beauty

Mr Clarke said the current rules result in a “Rip-Off Britain”, which forces customers to pay 30 to 35 per cent more for staples such as milk, bread and eggs if they shop outside supermarket trading hours. On a Sunday these traditionally run from 10am to 4pm or 11am to 5pm.

“I want the rules changed,” said Mr Clarke.

“Why is it right for a customer who wants to buy their milk, or eggs or bread before 10am on a Sunday morning or after 4pm in the afternoon have to pay 30 per cent more for their goods?

“That’s just fundamentally wrong. It’s an example of Rip-Off Britain.

“You can online shop which you can do any time of the day. We’ve got a two-tier approach to the Sunday shopping experience.”

The rules do not apply to convenience stores, an area where Asda is not as well represented as its rivals.

The country’s biggest supermarkets are split over whether to extend Sunday trading hours.

Leeds-based Asda and Bradford-based Morrisons have called for a review of the trading laws ​more than 20 years after legislation allowed stores to open legally on a Sunday for the first time.

Morrisons believes that customers want to shop at different times and it would support a law that is based on what customers want.

However Tesco and Sainsbury’s, which have a strong convenience store portfolio, are understood to support the current rules.

A Tesco spokesman said: “We know our customers appreciated the extra flexibility on a Sunday around the Olympics and would not be opposed to seeing this repeated, for example around Christmas.

“Such a decision is, of course, a matter for Government, striking the right balance between this extra flexibility and the growing number of ways there are for customers to shop already.”

Open Sundays, a group of retailers campaigning for reform, said the rise of online shopping means the current law is outdated.

The lobby group said: “Sunday trading reform would be good for consumers, good for the high street and good for shop workers.”

Asda and its main three rivals, Tesco, Sainsbury’s and Morrisons, are all finding life tough at the moment as they battle to win back market share from the discounters, Aldi and Lidl.

Asda has hit out against Tesco and Morrisons for trying to lure in customers by offering vouchers, which it sees as a short-term fix.

Mr Clarke said he is confident Asda has not broken rules relating to the treatment of suppliers after an official investigation was launched into practices at Tesco, which could be extended to other retailers.

Mr Clarke commented after the Groceries Code Adjudicator Christine Tacon said she had a “reasonable suspicion” that Tesco breached the rules.

At this stage the investigation will focus on Tesco only and will look into practices including delays in payments to suppliers.

Mr Clarke said he was confident his company had stayed within the code of practice. He said: “Yes I’m confident we are okay.

“If she (Christine Tacon) expands the investigation into all retailers, that’s her choice. Of course we will co-operate.”

Asked if it was just Tesco that is affected, Mr Clarke said: “It’s certainly not in our business. Dave (Lewis, head of Tesco) is as shocked as anybody.”

It was reported yesterday that Tesco has called on suppliers to cut prices to reflect falling inflation or they risk seeing their products delisted.