A word which once had a specific meaning has been transformed into a general term of abuse. It is, for both lovers of exactitude as well as trains, all very confusing. For example, a recent and well-received novel, Trainspotting by Irvine Welsh, contains no mention of trains and turns out to be about drugs and social decay on a Scottish housing estate. It is also safe to assume that Mr Adams does not in fact spend his spare time collecting locomotive numbers from the platforms of Belfast Central.
Trainspotting, in its new and wider sense, seems to mean dull, obsessive, possibly anal-retentive, scruffy (the word anorak is never far away), but harmless. A London Evening Standard guide to hip new words defined 'dweeb' as 'awkward male - probably a trainspotter'.
The paradox here is that there are fewer trains and trainspotters in Britain now than at any time in the past 50 years, and that trainspotters are the ultimate in innocuity. (Most of them, anyway: Michael Sams was a trainspotter before being given life sentences for the murder of Julie Dart and kidnap of Stephanie Slater.)
And yet they attract such hate] I went to see Ian Allan, the man who invented both the original phenomenon and the word, to see if he could shed light on the mystery. Trainspotting began in 1942 when Mr Allan was a 19-year-old trainee in the public-relations office of the Southern Railway at Waterloo. Tired of replying to letters from railway enthusiasts demanding details of locomotives, he suggested that the office produce a simple booklet listing their vital statistics. His boss was not interested, so Mr Allan decided to do it himself.
The ABC of Southern Locomotives was a simple pocket- sized index of engine numbers and types. At a shilling each, 2,000 copies sold out immediately. ABC guides to other railway companies soon followed.
Locospotting - Mr Allan's preferred phrase - was identified as a phenomenon in 1944, when a group of adolescent boys were arrested on the tracks at Tamworth, the nearest station on the west coast main line to Birmingham. Partly in order to teach safety to young spotters, Mr Allan started the Loco- spotters Club.
By the late Forties it had a quarter of a million members. In the Fifties and Sixties a million ABC guides, listing 20,000 locomotives, were being sold every year. The police had to be called in on holidays to keep spotters in order at such key stations as Willesden, Clapham Junction and Tamworth.
All of this made Mr Allan rather rich. Today he is chairman of the Ian Allan Group, which employs 350 people in enterprises ranging from transport publishing to hotels and fertiliser supplies. Turnover last year was pounds 30m. But the train- spotters, the foundation of this empire, have all but gone - Ian Allan thinks perhaps only 10,000 dedicated ones remain. The problem lies chiefly with the death of the locomotive. The 'units' that British Rail now deploys lack romance, and many of yesterday's spotters are now mature and studious railway historians.
Mr Allan has no idea why his creations attract such loathing. 'I suppose people just dislike people who are different . . . it seems to be because they wear berets and haversacks and dirty mackintoshes and cover them with badges.' Mr Allan likes trains, he insists, but is not a 'number taker'. Or a 'rivet counter'. Does he find trainspotters to be interesting people? 'Ummm . . . Pass.'
Nor could Mr Allan quite explain the secret attractions of number-taking. I turned elsewhere. The trainspotting editor of Viz magazine, Chris Donald (who owns three former railway stations) said: 'In some ways you can get as much from a train as you can from a woman.' He is married.
And so trainspotters remain safe to laugh at. Exclusively male, they are, perhaps, the last minority group that can be reviled without fear of opprobrium. But perhaps not for much longer. The trainspotter, it was recently revealed, may be psychiatrically challenged. Dr Uta Frith of the Medical Research Council's Cognitive Development Unit, has said that trainspotters and other obsessive collectors of trivia, may be suffering from Asperger's Syndrome, a mild form of autism.
The syndrome, identified by a Viennese doctor shortly after the Second World War, is characterised by social ineptness, an over-literal and pedantic approach to language, a lack of sense of irony or humour and obsessively pursued hobbies - finding, as it were, safety in numbers.
Trainspotters, of course, have reacted badly to this suggestion. Most of all they dislike the accusation of a lack of sense of humour. One spotter recently gave an example to rebut the claim. A locomotive called Thor pulled up at a northern station. By the time it left, spotters had inscribed a new name in the grime - 'Thora Hird'.
Mr Allan defends the people who made him rich. 'The bulk of them are perfectly normal people, chartered accountants, engineers. It goes right down the scale to a few who are decidedly odd.' He avoids the latter. 'I usually go incognito to railway meetings. If I meet them and they want to discuss the relative merits of one class of loco or the other - I just say 'Can't we talk about something else?' '