Shares in J Sainsbury plunged by nearly 12 per cent today after Robert Tchenguiz, the Iranian-born entrepreneur who owns around 10 per cent of the supermarket group, sold his holding in pub chain Mitchells & Butlers (M&B), which raised fears that he could dispose of his Sainsbury's stake.

Times Online revealed this morning that Joe Lewis, the British billionaire, has bought the 25 per cent holding in M&B from Mr Tchenguiz for £137 million.

Mr Tchenguiz's stake in M&B was backed by struggling Icelandic bank Kaupthing.

J Sainsbury, which reported its first-half results today, cautioned that it expects the "challenging" environment to continue into the second half of the year.

The UK's third largest supermarket group's stock fell to 279.5p, despite posting second quarter like-for-like sales up 4.3 per cent at the top end of analysts' expectations.

Justin King, chief executive of J Sainsbury, said: “The economic environment remains particularly challenging and we expect this to continue throughout the second half, but we have developed the Sainsbury's offer to perform in these conditions.”

Mr King admitted today that the banking crisis has “significantly constrained” the retail sector and said that food inflation had gathered pace in the second quarter.

But he added that the supermarket's customers were increasingly turning to its own brand products to save money, and said its "basics" range had grown by 30 per cent in the 16 weeks to October 4.

Like-for-like growth in sales continued from the first quarter and revenue over the first half grew by 3.9 per cent, excluding fuel. Total sales for the second quarter were up by 8.4 per cent.

Supermarkets have proved relatively resilient to the credit crisis, despite many consumers tightening their belts. Last week Tesco, the biggest supermarket group, posted a 4 per cent rise in like-for-like sales, excluding fuel, for its latest trading period, while Wm Morrison reported an 8.2 per cent increase last month.

Earlier this week, data obtained by The Times from CACI, the market research company, suggested that J Sainsbury faces an increasing fight for shoppers’ spending in its London and Home Counties heartlands from discounters, such as Aldi and Lidl.

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