A British teenager, apparently inspired by an ancient fertility symbol, has painted a 60-foot phallus on the roof of his parents million-dollar mansion, a newspaper has reported.

Rory McInnes painted the huge genitalia on the recently-finished apartment roof of his parents' house in a village 100 kilometres west of London, The Sun tabloid said.

Click here to see the picture on BBC's Newsbeat

When contacted, Rory's father Andy McInnes first dismissed the report as a joke.

"It's an April Fool's joke, right? There's no way there's a 60-foot phallus on top of my house," Andy McInnes is reported as saying.

When Andy McInnes contacted his son, who is spending a year travelling, the teen reportedly replied: "Oh, you?ve found it then!"

According to reports, the 18-year-old student said he had decided to paint the massive mural after watching a documentary about the satellite images on Google Earth. Rory claimed the artwork would make his parents' home stand out.

The painting remained secret for a year before being 'discovered' by a helicopter pilot.

Rory's parents were not keen on the idea of their rooftop art acting as a fertility charm.

"We don't want any more children, so the idea of sleeping under a giant fertility symbol is rather worrying," said 49-year-old Clare McInnes. Her husband added: "When Rory gets home he will be given a scrubbing brush and white spirit and he can go and scrub it off."

Rory's efforts are a copy of a well-known feature of the Cerne Abbas Giant, a 55-metre figure of a naked man which is carved into the side of a chalk hill in Dorset, southwest England.