The comedian and Doctor Who actress plays a randy maths teacher called Michelle in West End show Under The Blue Sky.
And the 40-year-old mum-of-one must strip off for a graphic sex scene.
She doesnt apologise for having slept with all these people, Catherine tells The Sun.
I think its very honest and refreshing to have someone who goes, Yeah, I have a lot of sex.
'It just strips away the nonsense.
Catherine has just finished filming as assistant Donna Noble in BBC1 programme Doctor Who.
More than 10million viewers watched her become the first woman to turn into a half Time Lord.