There's always someone willing to take advantage of a good crisis, isn't there?

British railway passengers could be subject to airport-style screening at intercity stations, under plans being considered by the European Union in response to the Arras train attack. Train operators could be obliged to introduce surveillance cameras in every carriage and stations instructed to install scanners for passengers boarding high-speed trains, under options being discussed following the foiled attack. For the first time, Brussels officials are drawing up plans to create common EU rules on railway security. At the moment it is a national competence.

Before deciding whether to let the bureaucrats in Brussels make the rules it's necessary to work out whether the rules themselves make sense. That is, let's test the competence of the proposed rule makers, shall we?

Fortunately we've a method that allows us to do this: cost benefit analysis. Predictions are that soon enough we'll have some 1.4 billion high speed rail passenger movements each year in the EU. So, if we're to scan passengers, that means 1.4 billion passenger scans. Say, given the inevitable queues, this costs each passenger 10 minutes. And let's simply ignore the cost of the scanners and the people to man them. 14 billion minutes, 230 million hours, that's quite a lot of time being spent there. And we should value time at something....the Sarkozy Commission recommended that this sort of time should be valued at "undifferentiated labour rate" or minimum wage for ease of calculation.

230 million hours at, say, 7 euros an hour? That's €1.6 billion euros a year, just in the time spent being and waiting to be scanned. Hmm...and so what's the benefit?

Well, in order for this to be of benefit overall we've got to look at what will be saved. Lives, presumably. And we do know the statistical value of a life. Around and about €5 million in fact. That means, that to be of benefit, these scanners must save 320 lives a year. Each and every year.

Do we have 320 people a year being killed by terrorist attacks on trains? Are we likely to? Not that we can see it has to be said.

So, rather than imposing all of this cost on the good people of Europe it would seem more sensible to simply stay with the system we have. Punch any bearded nutters who start waving AK 47s around. After all, we do have good evidence that the current system works.