Miley Cyrus is making X Factor bosses nervous ahead of her performance on the show tomorrow.

The "Wrecking Ball" singer has reportedly been told to tone down her act for the family-friendly show after her controversial twerking at the MTV Video Music Awards with hitmaker Robin Thicke. "Miley seems to be on a mission to be as controversial as possible so everyone's a bit nervous. She's been told to tone it down for The X Factor. That said, we're not stupid," a source said.

Although big bosses don't want the performance to result in complaints, head judge Gary thinks 20-year-old should include her controversial rump-shaking move "It's music - she's a young girl. If that's the way she wants to express herself, fair enough. It's a tricky one because I remember Madonna when she brought her Sex book out and everyone was going crazy. That seemed more shocking. But, you know, there's an off button. I always say, if you don't want to watch it, turn it off," he said earlier in the week. "These singers are young, sexy girls - of course they are going to express themselves like that. But I don't let my kids watch it. I probably wouldn't let them watch anything like that, it's too sexual for them," he added.