Britney Spears' comeback has been delayed. The 26-year-old star's new single 'Womanizer' was due to air on American radio on Monday but record bosses have decided to hold it back because they fear it is not yet good enough to be a hit.

A source said: "The label held the song back to make it as great as possible." Earlier this week, an unfinished version of Britney's eagerly anticipated comeback single was leaked on the internet.

Footage of the star - who scooped three prizes at the recent MTV Video Music Awards - rehearsing the song in a Los Angeles studio was posted on video sharing site YouTube. Fans' reactions to the track were said to be poorer than expected, resulting in Britney's team deciding to return to the studio to improve it. 'Womanizer' is set to hit UK shops on November 24, with Britney's sixth studio album 'Circus' available one week later.

Meanwhile, 'X-Factor' judge Simon Cowell has confirmed Britney will perform 'Womanizer' on the UK TV talent show. Simon said: "Yes, I think Britney Spears is going to perform. We're absolutely thrilled to have her.

She's a hugely talented person. Everyone wants to work with her because she's a star. "The fact that she goes a bit crazy occasionally makes her more interesting. If she wants to shave her head before she comes on the show, she's welcome to.I don't care."