Marks & Spencer will announce a plan today to sell branded food at all its stores in an attempt to close the gap with Waitrose, as the upmarket grocers moved closer to a price war.

The move comes as analysts expect M&S today to report profits of £285 million for the first six months of the year, against £297.8 million last year.

M&S has been lagging its premium rival in sales growth since Waitrose introduced a value range to lure thrifty shoppers. M&S hit back this week with its first price comparison advertisements, pointing out products where its value “Wise Buys” were cheaper than Essential Waitrose.

It will roll out a pilot to sell branded goods to all its stores in Britain, excluding franchised travel stores.

Sir Stuart Rose, the M&S executive chairman, said: “Our trials have shown us that an edited selection of branded grocery and household products has a place at Marks & Spencer. Our customers are at the heart of this decision — they lead increasingly busy lives, so buying those essential, must-have branded products at M&S will help to save them time.”

The radical move may improve the leadership credentials of John Dixon, executive director of food, who is the leading internal candidate to become chief executive, allowing Sir Stuart to become a non-executive chairman.

Mr Dixon said: “My team and I are focused on delivering the best that M&S Food can offer — innovative products that provide unbeatable quality and great value. But there are some products that we could simply never compete with.” He cited Marmite, made by Unilever, and Nestlé’s Kit Kat as examples of goods impossible to replicate. Other branded goods that M&S will stock include PG Tips tea bags and Jameson Irish whiskey.

During the trial, the branded goods were supplied in a deal with Booker, the wholesaler run by Charles Wilson, a former M&S lieutenant of Sir Stuart. The arrangement is under review for the roll-out.

Greg Lawless, retail analyst at Collins Stuart, said: “If they want to be a convenience store, they have to do it. Overall, I’m still of the view that it isn’t the answer and I’m yet to be convinced of the economics.”

Last month, the M&S boss appeared to play down the threat of Waitrose, which is joining M&S in the convenience sector via a tie-up with Boots UK and with plans to open up to 300 stores, but he hinted at M&S adopting a more aggressive strategy: “If they [Waitrose] want to move into the convenience market, that’s their business, but M&S has got plenty of bullets left to fire,” he said.

This week M&S launched high-profile price comparison adverts, under the headline “Price checked against Waitrose Essentials. Quality checked by M&S”. An M&S spokeswoman said it was the company’s first price comparison advertisement.

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