This is the first time the Danish museum has agreed to lend pieces from its collection to an exhibition abroad. The cars in question were all produced by Lego in the course of the last 50 years.

“We’ve always maintained an excellent relationship with the museum,” said Jozef Heylen, director of the Mechelen Toy Museum. “That’s how we managed to get their agreement to release a number of pieces. That was an extraordinary privilege because normally they never lend pieces out.” The loss was discovered when the pieces were being packed up to be returned to Denmark.

“It’s a mystery,” said Heylen. “We have guards and security cameras, and all of the display cases are locked. The only possibility is that the models disappeared during the dismantling of the exhibition.” Because of the intricacy of some of the pieces on show, it took more than a month to take down the exhibition, he explained. “But it’s impossible to say exactly when they disappeared.”

The models appear to have been stolen by someone who knew what they were after. There is a growing market among collectors and, unless the pieces are extremely exclusive, they are almost impossible to trace. “Our museum has always had an irreproachable reputation,” said Heylen. “Let’s hope that doesn’t change because of this one case.”