Diana Rigg in her 1977 Series, Three Piece Suite. (Sketch: Screen Night, from episode 1.)
There’s no body double. There may or may not be a visible nipple, but that’s her firm and substantial breast out there for our viewing pleasure.
It is a smooth single take. The live audience reacted appropriately. Gotta love the BBC – there are two other topless women in the same scewe.
In a related scene (same character, different scene):
It’s weird to hear Diana speaking in a nasal voice with a bizarre accent (not sure whether it is supposed to be American).
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From the comments and e-mail (thanks, you guys):
You can see the clip in this video, starting at the 2:39 mark.
This imager did a thorough collage that shows the sequence:
