The private equity consortium circling UK retailer J Sainsbury has less than six weeks to decide whether to launch Europe's biggest buyout after takeover regulators today issued a "put up or shut up" deadline at the request of the retailer's advisers. The news came as property investors Robert and Vincent Tchenguiz revealed they had almost doubled their stake in the supermarket operator.

The move by the UK Takeover Panel, which today set an April 13 deadline for the consortium to declare its intention to bid or walk away for at least six months, comes just over a month after three of the four private equity firms revealed they were weighing a potential approach for Sainsbury's.