To look at him, Richard is a perfectly normal mid-30s male.

He dresses okay, works for a large publishing house, likes beer and football (but not to the exclusion of his lovely wife and two children, to whom he is devoted).

But beneath this perfectly normal exterior, there lurks a hidden obsession, which involves endlessly scribbling down numbers, taking photographs and making totally unnecessary journeys.

To his acquaintances, Richard is great company, funny, interesting, interested etc. etc.

But to his close friends, he is a train-spotter.

The obsession began when he was a child and his totally normal and non train-spotting parents decided to appoint a godfather, whose idea of treating the boy was to take him on a day trip to Edinburgh, where they would change platforms and return home again, marking the distance between telegraph poles as they went.

The godfather succeeded in instilling a passion for trains which stayed with Richard throughout his youth and into adulthood.

While other teenage boys were forcing their neighbours to consider moving with stereo systems and trying to impress girls with the size of their speakers, Richard would invite members of the opposite sex on a date which involved taking the train to Littlehampton, admiring the junction at Ford and yearning to sit with the driver.

When Richard and a group of his teenage friends were arrested for abseiling down the side of a viaduct, Richard was able to get them off the hook by explaining that they were just trying to secure a good vantage point from which to watch some particular type of engine which would be making its way along the line to get to a maintenance depot somewhere or other.

Landing a job in London and being sentenced to commuting for the rest of the foreseeable future (he's so far served 15 years), has done nothing to dampen his enthusiasm for his hobby and, despite the fact he notches up an average of 16 hours a week trying to get to and from work, he still thinks nothing of spending the weekend on a train to Manchester or Birmingham if he hears there's a particular engine to be photographed.

He even had a little trip with a couple of other "enthusiasts" planned - to Slovenia. They were going to take a trip along the coast and up into the mountains, on a type of train no longer used anywhere else in Europe.

But this morning he was extremely worried that his spotting days were numbered.

"Has Kim finally realised she's married to a freak and put her foot down then?" asked Mark, sympathetic as ever.

No, Kim understands," said Richard. "It's the authorities we're worried about."

He went on to explain that the arrest of several plane-spotters in Greece for spying, while they claimed they were simply taking photographs of planes - which is, after all, what plane-spotting is all about - had caused him and his friends to think twice about the trip.

"Well you can see their point," said Mark. "How could anyone who is not British understand that a seemingly normal group of males would want to spend their time photographing trains or planes for pleasure?"

"You're right," I said. "And think, Richard, if you were caught abseiling down the side of a viaduct now you could be arrested on suspicions of terrorism."

Richard nodded gloomily. The future for train-spotters, it seems, is not looking too bright.

But then he managed to cheer himself up with a thought.

"Ah, well," he said, a bit more brightly. "At least I still get to train it to work every day.

"And next week, I've a conference in Newcastle to go to ... "