Some lives are so intertwined with work that it is impossible to tell them apart. The backroom slaves who devote themselves to a company are harmless enough. But what of those rare titans who are synonymous with their business – the Richard Bransons or Rupert Murdochs of this world? Fitch, a rating agency, puts Berkshire Hathaway's Warren Buffett unequivocally in this camp. Along with downgrading the insurer by one notch on Friday, Fitch reiterated its “l(fā)ong-standing concerns with respect to ‘key man' risk in the form of the company's chairman”.

Whether or not Mr Buffett is in fact as irreplaceable as it suggests is beside the point. The effect on Berkshire's share price if Mr Buffet were to fall under a lorry or suddenly decided to retire to Tahiti would be catastrophic. But the reality is that one day he will not be around.

How, then, should publicly-listed firms such as Berkshire – or to a lesser extent Apple, whose shares tanked when fears were raised about Steve Jobs's health – plan for this eventuality?