Thomas the Tank Engine, the cleanest-living locomotive on the track, would not approve. Train sets on display at the International Toy Fair in Germany include scenes of policemen raiding brothels, battery-driven copulating couples and round-ups of immigrants. There is trouble in Toyland.

Part of the attraction of model trains has always been the order of the landscape. The trains may sometimes fall off the rails but on the whole they run on time. Everything is prim and proper: the plastic fir trees are untouched by climate change; the towns are tidy clusters of gabled homes rather than slum tenements and the little people never talk back.

Little wonder then that train sets appeal not only to children but to adults searching for a safer, more controlled existence. Frank Sinatra was a fan and his heavies would deal with anyone who mocked his hobby. After a nervous breakdown Walt Disney retreated from film-making to model trains. Phil Collins has a set; Neil Young bought an American model train company. Gerhard Schröder, the former Chancellor of Germany, used to sell train kits: one of his ministers had a layout in his attic. Hornby engines moulded the childhood of a generation of British politicians, bankers and generals.

But visitors to the trade fair in Nuremberg have been gaping at the antics around the railway lines. Merten, which makes train-set figures, is offering a nudist beach, a waitress wearing only an apron and stockings and a couple of lascivious pole-dancers. One scene shows a man urinating against a wall, watched by a woman. Another shows a couple performing oral sex. Look carefully at the scene depicting a brothel raid and, behind the naked prostitutes, you will see the figure of a priest trying to make a quick getaway.

Steamy, irreverent stuff for the train set veterans. Sometimes the Lilliputian world of Exhibition Hall 4A resembles a splatter movie rather than a children’s paradise. A horse is about to be battered to death with a hammer by a butcher. A worker at the blacksmith’s appears to have lost an arm. Blood is spread around liberally. Near a castle, a squad of soldiers have just executed a man. And that’s just the start-up kit.

“It’s a brave and depraved new world,” said Der Spiegel, a magazine not easily shocked. Rolf Fleischmann, heir to the Fleischmann model-train dynasty, has a sober, commercial explanation. “We’re trying to make people chuckle,” he said. “You see so many poker-faced collectors in their 50s and 60s who make their trains operate according to their own tightly worked out timetables, and we just wanted to show, especially young people, that it can be a more relaxed world.”

That means introducing more aspects of real life. There are trains carrying nuclear waste — watch that one crash — and freight trains carrying the German Army on combat missions abroad. “Not the Third Reich though,” Mr Fleischmann emphasises. “We don’t do the Third Reich.”

Model trains now come with authentic noises. With the appropriate loudspeakers the nursery can sound as convincing as Clapham Junction. The blend of reality and fantasy, however, confuses German commentators. The pastoral idyll of the landscaped train set has always led to disappointed collectors, says Dirk Kurbjuweit, of Der Spiegel,because the real world was so much worse. “Now Fleischmann is turning the tables — spend a few hours playing in the horrible world of the toy fair and you’ll be glad to return to everyday life.” On track

The world's largest model railway is Hamburg's Miniatur Wunderland, with 9km of track and 700 trains

The hobby began in the heyday of the steam age in the 19th century, but did not take off until electric models were introduced. The oldest society devoted to the pastime is the Model Railway Club in London, founded in 1910

One of the most famous layouts is Pendon Museum’s Madder Valley in Oxfordshire. An intricate rendering of a fictitious valley, it took one man nearly 20 years to complete

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