The police leap into action

The gates out of Trafalgar Square under Admiralty Arch were closed last night. That's not happened in the six months I've been driving home along that route, but there's always a risk of it – in much the same way there's always a risk that you'll blow your eyeballs out when you sneeze.

It probably won't happen. But it might. And tonight, it did – the gate part of it, anyway. Not the sneeze.

I pulled up in a small queue in front of the gates, just three cars, and sat there stupid with tiredness, wondering what would happen next. The first car was a taxi, and I quickly saw the driver was on his feet wrestling with the gate, which was heavy black metal and at least three times his height.

Slowly it swung open, and equally slowly I remembered something I'd seen out of the corner of my eye as I'd pulled up. A flash of yellow from a reflective jacket. I looked over my left shoulder – and there was a policeman walking towards us with steady, measured steps.

Having to turn away and find another route west out of the square would have been a real inconvenience, so I watched anxiously, waiting to see if the policeman would order the taxi driver to stop.

And then I realised that, although the policeman appeared to be striding purposefully towards us, he was actually covering ground very slowly. And meanwhile, the taxi driver was almost done. The copper had, in fact, calculated exactly the speed he needed to walk in order to appear to be acting but actually arrive just too late to have to intervene.

He was about three foot from my rear bumper when the taxi driver got back into his vehicle and we all disappeared through the now-open gate. In my rear mirror I saw the policeman stand in the centre of the arch, staring stoically up at the great gateway. He made no attempt to close it again.

I dare say that after a moment or two had passed he was off, boldly marching off to arrive somewhere else just in time to not have to do anything.