Police are investigating a rape threat against Cheryl Cole made in a message left on Dermot O’Leary’s mobile phone.

The X Factor presenter was believed to have raised the alarm after picking up the threat on his voicemail left by an unknown caller.

A City of London Police spokesman confirmed an investigation had been launched into an ‘offensive message’, saying: “We are investigating claims of an offensive message being left on a mobile telephone. It follows a complaint from a member of the public.”

Dermot, 36, joined the ITV show in 2007, a year before the Girls Aloud star’s arrival as judge.

Security for The X Factor judges was apparently increased in 2008 after a tracking device was put into Simon Cowell’s car.

Cheryl has been alerted to the threat, according to the Sun.

The singer was appearing on Fearne Cotton’s Radio 1 show on Tuesday morning.