Over the past year or so, what appears to be a fairly mundane and inoffensive question has become the question of choice for Select Committee members; Public Inquiry chairmen and their QCs; Opposition MPs in the Commons; and, at the front of the queue, BBC presenters.
Those subjected to the interrogation are invariably senior members of Government, public institutions or private companies, summoned to account for themselves in the wake of the latest in a seemingly never-ending series of issues of public concern. In the firing line yesterday were the CEO of security firm G4S and the Governor of the Bank of England. The former had been charged to attend the Home Affairs Select Committee, to explain the failure of his company to provide the contracted numbers of people to secure various Olympic venues. Meanwhile, the Bank of England chief was being quizzed on the banking crisis in general and the manipulation of the inter-bank lending rate in particular. Other recent examples include inquiries into the take-over bid for BSkyB, and the phone-hacking scandal.
In all of these cases and others, "When did you know?" has been used relentlessly, and with accusatory zeal, in an effort to 'prove' the incompetence or, worse still, dishonesty of those on the receiving end of the question.