Scenes from Turnpike Lane station...

An hour ago, on emerging from the bowels of the Picadilly line as is my wont at half six on a Thursday, I was dismayed to see a wall of armoured police surrounding a pair of electronic weapons-detecting barriers through which the good residents of Wood Green were being made to walk. So I took it upon myself to engage a couple of members of Her Majesty's Constabulary in conversation.

'Why are the scanners up again?'

'It's a deterrent. You know, knife crime. You watch the news, don't you?'

'So what are they for?'

'Well, to see if anyone's carrying a knife.'

'Is it against the law to refuse to go through, then? Say, what would happen if I just walked right round the edge?'

'Well, you're not exactly carrying a knife, are you?!' Sner sner, oi lads look at the sweet little white girl in her cardie trying to be clever.

I tried a different tack. 'So, how do these barriers tell if you're carrying a knife rather than just, say, any old metal?'

'They don't. They're quite neanderthal really. They just flash red when someone's got metal.'

'But hang on. The lights are flashing red for every other person. Why aren't you stopping all those people?'

'Well...' indulgent little police-officer smile turns into get-rid-of-this-member-of-the-public grin 'look, we just use our judgement - say, if someone like your good self set off the buzzers, well,' looks me up and down 'you're clearly not the sort of person to be carrying a knife, are you?'

'So what sort of people would you stop and search, then?'

'Well, you watch the news.'

'Of course I watch the news. What sort of people would you stop?'

'You know, the sort of people who commit crimes. You watch the news.'

'You haven't answered my question.'

'Are you a journalist?'

'Absolutely.'

'My colleagues and I aren't trained for this. Bugger off and call the press office and go through those barriers while you're about it.'

Stunned, I marched through the ancient plastic barriers, the metal buckles on my boots winking.

And the lights flashed red.

And nobody stopped me.