Since 2001 a new disease has been growing. It is not infectious, nor can it be transmitted by person-to-person contact. The causes are not well understood, and the disease is indiscriminate, occurring in sudden, isolated outbreaks. In the UK each year it kills approximately 50 and affects maybe 150 more, affecting 0.0003% of the population each year. You probably don’t have it.

Roads, alcohol, falls, and fires all kill more people each year. We accept these risks. There were 6,769 deaths directly attributed to alcohol in 2008, but it won’t stop us drinking. Police estimate 730,000 people are killed or injured in road collisions each year – 3,500 times as high as our mystery disease. A big figure, but we accept it. We know the roads are dangerous, but we’ll still cycle to our lectures and drive up and down from Oxford with car-loads of stuff.

So how much money should we put into treating this new affliction? Let’s pick some upper boundaries. Clearly more money should be spent on treating circulatory disease and cancer – two of the biggest causes of death in the UK. Perhaps, more money should be spent on making our roads safer: the cost of injuries and deaths on our roads is put between £15-32 billion. Treatment of a minor disease that affects so few people each year should pale in comparison.

Now suppose there is a treatment for this disease. It is not completely effective, and it comes at the expense of certain civil liberties and massive financial cost. Should the liberties of 60m people be curtailed as a way of maybe saving 200 people a year? Clearly not.

The fact remains: the treatment of such a small section of the population must not be allowed to be detrimental to the lives of everyone else. Treatment like legislation that allows control orders or 30-day detention without trial. Or laws that allow police to stop innocent tourists taking photos in railway stations and other locations deemed ‘targets’. Or, in the United States, legislation signed into law already this year that, according to Human Rights Watch, “[codifies] indefinite detention without trial into US law for the first time since the McCarthy era”. Cite ‘national security’ and do as you wish.

The mystery ‘disease’ is terrorism, and we react to it unbelievably disproportionately – even though the comparative risks are vanishingly small. As long ago as 1993, a study by Eric Johnson, currently at Columbia Business School, found respondents would pay more for insurance cover against just terrorism than for either non-terrorism related cover or – astonishingly – cover for “any reason”. After 9/11, more Americans took to driving rather than flying. The result was an increase in deaths on the roads. Tragically, we accept this as a risk of driving in a way we do not accept the risk of terrorism. We prefer the risk of dying on the way home from work or the risk of detention without trial to the risk of terrorism.

Such fears are not just brought out by terrorism – though it’s there that the feelings are strongest. A report by the Police Federation on the fear of crime cites research in which high levels of investment reduce actual burglary rates by 42% – but the percentage of people worrying about crime actually increases by 7%. Despite the hysteria that surrounded the Fukushima power plant last year, a 2002 report by the International Energy Agency concluded that the deaths per unit energy output are far higher for coal than for nuclear power. An International Atomic Energy Agency report has argued that psychological issues are the most significant effect on health from Chernobyl. The MMR jab controversy dramatically cut inoculation rates, and in doing so put more people at risk. What do these have in common? Misunderstanding of risk.

These are big issues, and they have big consequences. The debates about how we are going to power our iPads, televisions and PCs in twenty years time is always going to be skewed if we cannot properly understand the risks to our health associated with nuclear power. Tackling ‘fear of crime’ will never be construed as a waste of money, in the same way that funding for counter-terrorism will always go up. When the terrorist attack comes, no prime minister wants to have to admit they cut spending to counter-terrorism units.

We react most strongly to specific, if unlikely, threats. Terrorism (or indeed nuclear radiation, or “autism-causing” MMR jabs) create these kind of threats. They are also massive media stories, inexplicable bringers of death. Hidden in our midst, invisible, able to damage us or our loved ones at any time, out of our control. And so we have to rely on our politicians to protect us. They may well protect us, but at what cost – and to whom?

The threat is real, but it is not what we think it is. The greatest risk is not from terrorists or nuclear power stations or murderers. We’re much more likely to get killed crossing the street or cycling to lectures. The real threat is the consequences of our misunderstanding of these risks. The loss of civil liberty, the drop in vaccination rates, the lack of coherent and sustainable energy policy: these are real problems that will affect us all, unlike the fears that hover around them. It’s not the terrorists we should be scared of. It’s the bigger, quieter killers that happen so often they become normal.