Why surprise to fight crime works

However, smart-thinking cops have found other innovative ways to tackle the problem. In 2012, Met Police officers used a borrowed No. 2 London bus to sneak up on a gang of street gamblers on Westminster Bridge. Normally, the lookouts alert the street gamblers well in advance but, on this occasion, they hadn’t anticipated the 30-plus officers who jumped out on them as the bus came alongside. More than 25 gamblers were detained and 12 were charged with gaming offences.

Predictable policing is useful to criminals. Predictable audits are useful to fraudsters. Predictable parents are useful to teenagers with access to the drinks cupboard.

Any defence eventually publishes an unofficial instruction manual. The inspector always comes on Tuesday. The manager checks the figures at month-end. The phishing test arrives at 10am from an address that may as well be [email protected]. People do not defeat the control; they learn its timetable.

The bus worked because it made the lookout’s expertise briefly worthless. He knew what police looked like when they arrived, so thirty officers arrived looking like public transport. That is the delicious bit. More uniforms, sterner posters and a larger committee would have strengthened the expected pattern. The Number 2 bus punctured it.

The same principle explains why the least impressive-looking security measure can be the most effective. A nightclub may have a large doorman at the entrance and a quiet woman inside who notices everything. Guess which one the regular troublemaker has already planned around. Visibility reassures the innocent; uncertainty troubles the rehearsed.

Serious systems need steady rules and restless methods. Keep the standard; vary the footprint. Inspect the quiet branch. Ring as an ordinary customer. Test the refund at 4.55pm on Friday, when values tend to become negotiable. Change the route until everyone has to follow the rule on ordinary days too.

Surprise can become managerial sadism if it is used to keep decent people anxious. That is lazy too. Aim it at rehearsed compliance, not human nerves. A control announced three weeks ahead measures preparation for the control. What happens on the unremarkable Thursday nobody circled in advance?