The private equity consortium at centre of the takeover speculation surrounding UK supermarket group Sainsbury is facing an ultimatum to make a formal bid in the next few days or back off. The UK's Observer newspaper reported on Sunday that the Takeover Panel is to call the consortium, consisting of Kohlberg Kravis Roberts, Blackstone and Texas Pacific Group, to end the uncertainty over its intentions. Sainsbury's share price has risen sharply in the last month since news of a possible bid surfaced. But there has been little movement towards an actual offer.