Sainsbury’s profits edged up in the first half of the year as more customers opted for bigger baskets and shopped the grocer’s premium range.

In the 28 weeks to 14 September, retail underlying profit increased 3.7% to £503m and grocery sales rose 5%, while the supermarket claimed to be “delivering the biggest market share gains in the industry”.

It comes as more customers are going to Sainsbury’s for a bigger food shop and nearly two thirds of big baskets include the retailer’s premium Taste the Difference range, with sales of the own-brand up 18% in the quarter.

Sainsbury’s added that the key to winning more big baskets has been a step change in its value perception, as it has invested £1bn in value in recent years.

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Sainsbury’s chief executive Simon Roberts said: “Our food business is going from strength to strength and we’re making the biggest market share gains in the industry, with continued strong volume growth. More and more customers are coming to us for their big food shop, recognising our winning combination of value, quality and service.

“Reflecting our leading quality, more customers are choosing Taste the Difference, with sales up 18%, the strongest premium private label growth in the market. And with the biggest ever increase in customers’ value perception, we’re outperforming the market across the whole basket, particularly in core fresh food categories.”

He added: “With strong momentum and increasing confidence in the strength of our grocery offer, we’re now investing to bring the best of Sainsbury’s to more people in more locations, including the recent acquisition of eleven Homebase and two Co-op stores.”

Over the next 18 months, the grocery retailer expects to open around 20 new supermarkets and 20 to 25 convenience stores.

Looking ahead, Roberts said Sainsbury’s is expecting “another strong performance” as it gears up for the festive season, and longer-term the business remains “confident of delivering strong profit growth in the full year”.

Combined with continued growth in Nectar profit contribution and delivery of cost savings, the supermarket giant expects to deliver retail underlying profit of between £1.01bn and £1.06bn, growth of between 5% and 10%.