Teachers thought they had seen every penis prank. Phalluses have always been scrawled on textbooks and chairs, and special points were awarded for arranging a penis on the blackboard behind an unknowing teacher’s legs.

But the graffiti was on a relatively small, and private, scale. Thanks to Google Earth and Google Street View, dubious artwork can reach a wider audience.

A penis discovered on top of a house should send out warning bells to schools. Teenager Rory McInnes, who painted a giant phallus on the roof of his parents’ Pounds 1 million West Berkshire mansion, was apparently inspired by a programme about Google Earth.

But schools have already been hit. In 2006, The Sun reported that “pranksters drew a willy on the roof of a top school” in Teesside that went unnoticed until it appeared on Google Earth.

And a pair of unnamed Year 11 pupils from Bellemoor School in Southampton etched a giant penis on a school lawn using weedkiller in 2005. Satellite images cropped up on the internet two years later.