The increase has fuelled speculation that Qatari investment company Delta Two, which recently acquired 25 per cent of the retailer, is poised to launch a takeover bid.
Tchenguiz is understood to have increased his stake in the supermarket to 11 per cent, up from 5 per cent. He bought the£350 million holding via derivatives known as contracts for difference.
It is thought that he is not working with the Qatari royal family's investment vehicle, but that he views his stake as a long-term investment.
The increased stake would give Tchenguiz more clout to push for changes to the supermarket's property portfolio, which he regards as undervalued. Tchenguiz also owns a one third stake in rival grocer Somerfield.
Earlier this year, Sainsbury's rejected a 582p per share offer from a consortium led by CVC Capital Partners.