Going further, to criminalise, would simply create a culture of fear in which a cascade of tiny suspicions would overwhelm the system and obscure more well-founded concerns.

During storms, for example, high levels of rainfall (in excess of 6 mm per hour) in a short period of time can overwhelm the system.

But record numbers of students have overwhelmed the system with a million applications.

Settlement by physical delivery of certificates worked adequately until the 1960s, when a sharp increase in trading volumes overwhelmed the system.