A 12-year-old boy was called an "ugly tw*t" by an iPhone 4S. He was testing the smartphone in Tesco.

Apple's recently released handset boasts Siri, an intelligent software feature that answers questions.

However, when Charlie Le Quesne asked the phone 'how many people are in the world?', the mucky-mouthed mobile responded with "shut the f*ck up you ugly tw*t".

The child's mother complained to staff, who apologised and blamed the phone's profanity on pranksters who had tampered with the device's setup.

"The phone was a demo version and was low enough on the shelf for Charlie to have a go on it," said his mum.

"He asked it a simple question and we couldn't believe the filth it came out with. I thought I must be hearing things. So we asked again and the same four-letter stuff blared out. I asked for the manager and after staff heard it they agreed to unplug it."

A Tesco spokeperson said the company had launched an investigation into the incident.