Kevin Spacey has offered to perfect his famous Johnny Carson impersonation for a planned Tv biopic, but only if the script is as edgy as it should be.

The Oscar winner is famous for his take-off of the late Tv mogul, but he hasn't yet been approached for the upcoming NBC mini-series, and he insists he won't even consider the project unless the screenplay is appropriate.

He tells The Hollywood Reporter, "If (Nbc) wants to start writing as if they're a cable network, then absolutely I'd do it, but I'm afraid it would just be too marshmallow, and Johnny deserves something that's tougher with more expletives."