Former pop princess Britney Spears is giving Cowell, the brutal British TV celebrity judge, a run for his money in her new job on the panel of US talent show The X Factor.

"You can't destroy that song, sweetie", "predictable" and "I want to know who let you on stage" were just some of the remarks made by the 30-year-old singer to contestants during auditions for the TV contest, according to early promotions for its second season.

"Britney is quite mean, which I think you will discover," Cowell, the creator of X Factor, said on Monday. In fact, he joked, she is "as sweet as a lemon".

Spears signed on in May, joining former Disney Channel star Demi Lovato, 19, on the panel after both Paula Abdul and Nicole Scherzinger were fired following a disappointing first season.

"They are harder to please than me or [fourth judge Antonio Reid]," Cowell said.

Spears said she was "just a very honest person" who was eager to help young singers.

"I have done eight tours and I have been in the music industry for a while, and I think being able to give back is really interesting," she said, explaining her decision to accept the job for a reported salary of $15-million.