I know a wrong 'un when I see 'un

You can't always tell what a person does by what he looks like," said the elderly man in the train opposite me. "Take me, for example."

You can't always tell what a person does by what he looks like," said the elderly man in the train opposite me. "Take me, for example."

We had got talking when he had gone to the buffet for a cup of coffee and had asked me to look after his place. When he came back, he said he saw I had had no trouble in his absence.

"On the contrary," I said. "Several people laid hands on your copy of the Daily Mirror and I had a great deal of trouble persuading them to leave go. One of them even offered me money for it."

He laughed and sat down and we got talking, and he asked me what I did and I told him I was in the writing game, and he said, yes, I looked like a writer, and I said that wasn't true because if I did really look like a writer, he wouldn't have had to ask me in the first place, and he admitted that that was true.

"Yes, you can't always tell what a person does by what he looks like," he said, which was where we came in. "Take me, for example. What do you think I do?"

I looked at him. He was in his sixties, bushy silver hair, with rough but distinguished features. He could have been anything from a gamekeeper to a company director.

"Retired policeman," I said, at random.

He went off into a paroxysm of coughing and laughing. "That's rich!" he said. "I was involved in the law, but on the other side. Know what I mean?"

"Crime?" I said.

"Crime and time," he said. "Done me crime, done me time. I'm retired now. But I don't look like one, do I?"

"No," I said. "But then I have no idea what a criminal looks like. On the other hand, they say that a criminal can always spot a policeman in disguise - that there's something about a copper which sticks out a mile. Is that true?"

"Spot on," he said. "I'll tell you a funny story about that. I used to be quite close to a certain police officer - nothing crooked, we'd just done each other a couple of good turns - and he said to me one day, 'Dick, I wonder if you could help me out with an identity parade?'

"It turned out that they had a new intake of plainclothes officers, and my friend genuinely didn't know which ones stuck out as policemen and which didn't, so very sensibly he was going to an expert. Me. So I went in this room, and there were about 20 young blokes standing in a line, and he asked me to make a note which ones smelled of the police and which ones didn't.

"Well, I got the shock of my life about halfway along, because I recognised one of these geezers. He was a bloke called Charlie. Charlie Parsley we called him, because his dad was a greengrocer. He was a minor villain. I had done a job with him once. He wasn't a police officer at all - he was a wrong 'un!"

"So I looked at Charlie and he looked at me, and neither of us said anything, and I passed on, and my friend asked me afterwards if any of them had the smell of policemen about them, and I said one or two did, but I didn't say anything about Charlie, although I might have said he had the smell of a villain about him, but I hadn't been asked about that, had I?

"And after that I had to go inside for a while, and when I came out I bumped into Charlie again, and asked him if he was still helping the police with their inquiries, and he said he certainly was, and he had been promoted regularly, and was doing all right. And I said I had got the shock of my life at that parade, and he said he had too, and I asked him what the hell he was doing joining the police. Was he going straight or what? And he said, Had I never heard of a plainclothes criminal?"

The man in the train looked at me.

"Implying he had joined the police in order to get their secrets?" I said.

"Or to get the perfect alibi," said the man. "After all, who would suspect a policeman?"

"Everyone, these days," I said.

The man went off into more coughing and laughing, and then got off at the next stop.