Odds are funny things. Logically, we generally believe that if we have two options, where one option is twice as risky as the other but offers double the rewards, they are mathematically equivalent. Likewise, on the negative side, where you’re talking about dangers rather than rewards.

This reciprocal relationship tends to fall down at the extremes. If you know about photography and the relationship between lens aperture (f stop) and shutter speed, then you’ll perhaps know that there is such a thing as ‘reciprocity failure’: for most photographic film, extremely short shutter speeds require disproportionate aperture settings.

So when you’re talking about the infinitesimal chance of something infinitely horrible happening, emotions tend to kick in and override common sense.

These thoughts went through my mind shortly after discovering that British Airways flight BA874 from Heathrow to Moscow on 15th November and BA875 on the return journey two days later are on the list of flights that were potentially contaminated with polonium-210. I was on those flights. (Admittedly my thoughts of reciprocity failure didn’t occur tome straight away – it took several hours once I’d got over the shock of being even tangentially involved in the murder of Alexander Litvinenko.)

Now British Airways helpfully told me that the risk to public health is "very, very, very negligible". Strangely, that didn’t sound very reassuring, even though the chances of me being hit by a meteor while on my way to the bus stop are also very, very, very negligible. My chances of being killed in a car crash are fantastically greater, but I worry less about that. Perhaps it’s the spurious feeling of being in control while driving that makes those odds seem less significant than the chance of being inadvertently poisoned by Russian spies.

So it’s a funny thing, risk. I admit I felt a bit better when I found out (on a professional aviation website) that polonium-210 has alpha rays which can be stopped by a barrier as thin as paper, or even skin. You really have to swallow it for it to be harmful – and unless my flight companion was a rogue KGB agent intent on bumping me off, I would have to have done something as bizarre as licking the aircraft seat cover so as to ingest any secreted polonium in order to be at any real risk.

Still can’t get my rational side to overcome my emotions on this one, though. And for now I’m steering well clear of anyone carrying a rolled-up umbrella…