The Co-operative Group is poised to jump back into the supermarket big league by completing its long-awaited £1.6bn takeover of Somerfield.

Sources close to both companies said that terms had been agreed after months of talks and that an announcement should come this week.

The takeover would trigger a windfall for Robert Tchenguiz who holds a 30% stake in Somerfield, as well as his fellow shareholders Apax, Barclays Capital and Kaupthing, the Icelandic bank.

For the Co-op, the deal is central to its hopes of reviving memories of the 1960s, when the group, famed for its “divi” card, became Britain's biggest grocery retailer with about 13 million customer-members.