Black swans have taken their place in the investment menagerie, alongside bulls, bears and dead cats. It is barely a year since Nassim Nicholas Taleb’s best-selling book Black Swan was published, but the phrase has worked its way into the investment language.

And like other market concepts, it is already subject to abuse. Taleb took his title from the shock that Europeans experienced when they discovered black swans in Australia. Until then, their data told them that all swans were white, so the discovery was unexpected.