Dame Emma Thompson's family threatened to ''burn'' her piano when they got sick of her rehearsing for 'The Children Act'.

The 59-year-old actress - who has Tindy, 30, and Gaia, 18, with husband Greg Wise - portrays High Court judge Fiona Maye in the upcoming new drama and she admitted the emotional content took its toll on her and her loved ones.

She said: ''I was not grim, but less wild during this shoot. I had to perform a song. I was so nervous about it that I rehearsed so much my family said, 'If you play that one more time we are going to burn the piano and lock you out.' ''

As part of her preparation for the role, Emma spent hours at court and felt privileged to observe the lawyers and judges at work.

Speaking to HELLO! magazine, she said: ''It was one of the greatest privileges. Backstage [at court] only judges and clerks are allowed to walk on the red carpet. They are godlike creatures in their robes and hardly any women have that power in the world, ever. It was extraordinary to watch. Their level of work and brainpower is extraordinary. Then when I talked to them, my admiration extended even further. To combine that sense of power, that actual power with compassion - and one has four children and gets up at 4am every morning to do all the work so she can see them off to school - they are super-human to me.''

And Emma was surprised when her performance as her character was compared to a big screen superhero.

She said: ''I was talking to a young comedian about the film and he said, 'You're just like a Marvel superhero in the beginning - in the courtroom she's so badass.' I said, 'Like Superman in the third one where he goes over to the dark side?' I'd never thought of it like that - that's very illuminating.''