Although supermarket inflation in Great Britain decreased last month, households were boosting their grocery spending by stocking up on lunchbox staples.

According to retail researcher Kantar, the inflation of grocery prices decreased to 1.7% in the four weeks ending September 1st from 1.8% in the previous month. Nevertheless, nearly 60% of households expressed concern about the growing expense of their shopping.

Sales of fruit bars, cereal, and fromage frais increased by 14% during the last week of August compared to the same period last year, while sales of chocolate biscuit bars increased by 12% during the back-to-school season.

“The demand has picked up once again for lunchbox favourites as summer draws to a close and parents stock up ahead of the new school year,” said Fraser McKevitt, the head of retail and consumer insight at Kantar.

However, he said that, more broadly, shoppers’ financial confidence had not risen. “Memories of the last two years remain strong, with nearly 60% of shoppers still very or extremely concerned about rising grocery prices. This is their second biggest financial worry, only behind home energy bills,” he added.

Retailers are offering more deals to ease the burden, with the proportion of sales on promotion rising year on year for the 16th month in a row. More than half of all grocery trips include shoppers using some kind of deal, and this proportion rises as their spend gets bigger, McKevitt said.

Prices are rising fastest for vitamins, minerals and other nutrition supplements, as well as chilled fruit juices and chocolate confectionery, and are falling fastest for toilet tissue, dog food and bottled colas.

Grocery sales rose by 3% in value over the four-week period compared with a year earlier, down from 3.8% last month.

Ocado was the fastest-growing supermarket for a seventh consecutive month, with sales up 12.9% year on year. Asda was the worst performer, with sales down 5.6%. The Co-op was the only other big grocer to report a sales drop, of 0.7%.

Aldi, the German-owned budget retailer, said on Monday the slowdown was partly because big chains including Tesco and Sainsbury’s have won back customers by promising to match Aldi on key items.

Tesco, the largest retailer in the UK, saw a 5.3% increase in sales, while Sainsbury's saw a 5.7% gain.

Waitrose's sales increased by 4%, although Morrisons' lead was 2.7%. Sales at the cheap stores jumped by 9.1% for Lidl and just 1.3% for Aldi.

Shops are waiting to see how household inflows and outflows may be impacted by the chancellor's autumn budget, which is due on October 30.