The decision by Delta Two, an investment vehicle of the Qatari Investment Authority, to abandon its bid for UK retailer J Sainsbury has stretched credibility in ways so diametrically opposed it is hard to know what to anticipate.

First, what did the sovereign wealth fund think it was doing, negotiating with the company, its family and other shareholders and the trustees of the pension scheme, for months after the credit crisis reached boiling point in July, only to rescind its £10.6bn (€15.2bn) offer after running through its calculations again and deciding it would have to stump up an extra £500m?