X Factor judge, Simon Cowell is said to be furious after discovering a bug concealed on the undercarriage of his car.

The Mirror reports that Cowell asked his security team to search the Bentley Continental after he noticed that a leather-clad biker kept turning up wherever he was.

A source said: "He can’t believe someone has gone to so much trouble and expense to monitor his every movement. It’s extremely sinister.

"Simon has his suspicions as to who is responsible. He is so angry he is considering calling in the police to investigate further. It is a hassle he could do without – especially with The X Factor in its final stages – but it has to be done. He can’t take any chances."