Since 2008, we have developed a powerful faith in the skill of central bankers to perform emergency financial surgery. But bubbles are forming across global markets and, having performed every conceivable procedure, conventional or unconventional, it is hard to see what central banks can do when these bubbles burst.

It was five years ago this month that the Bank of England started quantitative easing and cut rates to record lows. Interest rates in major economies are close to zero, and central banks do not have much appetite for negative deposit rates. Quantitative easing has been tried and tried again, and unless central banks were to start buying equities (which is most unlikely), it would just be more of the same, have diminishing effect, and - in parts of the world - still face questions of legality.