...or in other words, people we perceive as strange, either in their dress, their speech or their behaviour. Slight eccentricity can be endearing or annoying, and no one thinks too much of it, but at what point does it become bizarre enough to be memorable, even fifty years later?

Last week I had an odd and slightly surreal conversation with a lady on the Downs. We both walk our dogs on this particular hill and often exchange a few words, but somehow, this time, the subject of eccentricity came up.

Once we began remembering these characters - often only seen in passing - it was amazing how many we had in common.

One of these was a man my brother and I named The German Spy. The logic of why a spy would wish to draw attention to himself in any way at all didn't enter our heads at the time. He used to stand next to the A27 - at a T junction if I remember correctly - near the old toll bridge at Shoreham. He was always immaculately dressed in tweed jodhpurs, matching tailored jacket and deerstalker, yellow waistcoat, cravat and long, brown, highly-polished riding boots. He may have been holding leather gauntlets, but these could be an imaginative delusion on my part.

He seemed to be posing - the image I have of him is with one hand on his hip, holding a monocle to his eye. Behind him, propped on its stand, I see in my mind's eye a powerful motorcycle with a smaller identical figure reflected in its gleaming chrome, but memory could well be be playing tricks on me, as the lady on the Downs remembers just a very clean bicycle.

As children, my brother and I would look out for him every Sunday on our way back from a family walk in the country - usually in the woods at Arundel - and wave out of the car window. I think he was pleased at this attention, as he used to preen a little and stand even straighter. Some motorists used to hoot, but it was all very good-natured.

He must have been around fifty then, so if he's still alive he'd be at least a hundred, but as I haven't seen him for many years now, I'd guess that he's no longer with us.

As I left the lady on the hill other memorable eccentrics came to mind, and I couldn't help feeling impressed at the ability of perfect strangers to leave such a lasting impression.

So... I have to ask myself: will the eccentric characters in my books survive in the memory of strangers? Perhaps it's time for me to wear purple...