Sainsbury’s shares hit a roadblock this week after a fantastic run over the summer and autumn months. The supermarket chain reported a 4% increase in underlying operating profit to £412m for the six months to 29 September.

It proved insufficient for investors, and the shares dropped 2.4% to 338.8p. “An excellent half for relative like-for-like sales and cost savings has led to zero progress in EBIT margins,” said Oriel Securities analyst Jonathan Pritchard.

In the run-up to Wednesday’s interim results, Sainsbury’s shares outpaced a buoyant FTSE All-Share, rising almost 25% from June to just over 360p at the end of October. Over the same period, Tesco shares rose 6% to 320p and Morrisons’ yo-yoed, ending virtually unchanged at 370p.

Until now, Sainsbury’s superior like-for-likes and market share gains has consistently boosted its share price. Similar progress is likely to be harder to attain over the coming months.

This week’s reported rise in inflation from 1.9% in September to 3.3% last month provided an unwelcome reminder to all the listed supermarkets of just how tough it is likely to be to make share price gains.

“It is just the start of a sustained re-emergence of food price increases, and we are of the view that they will reach at least 5% next year,” said Pritchard.

The analyst predicted further pressure on margins and an even harder fight to keep volumes from tumbling. “The average shopper does not have the extra £25 a month to spend on food that 5% inflation implies,” he said.

Morrisons’ latest move to reverse declining volumes - a 10% discount card for new shoppers in certain areas - failed to impress the City. Its shares closed down 1% on Wednesday as analysts attacked the initiative, warning that it could put off loyal shoppers and made little financial sense. “Today’s episode does not instil confidence,” said Shore Capital analyst Darren Shirley.

There was better news for investors in AG Barr and Britvic. The two companies finally agreed the details of a merger to create a new £1.5bn turnover giant to be called Barr Britvic soft drinks.

The removal of uncertainty around the deal prompted a 5% jump in Britvic shares to 387p and a 4% increase in AG Barr shares to 450.8p.