Overdriver

I am trying to identify a very bizarre clip from TV-AM that I think was screened in the mid-80s, I would say between 1985-1987; possibly earlier but I'm fairly sure it was around that time. I remember it being shown as part of a feature on Good Morning Britain but was only a kid when I saw it, so can't remember all that much, but as a collector of surrealist movies and TV I'm pretty curious to identify it...

The clip involved a mother and boy at a swimming pool. It was a bird's eye shot of a busy outdoor swimming pool, and to the left of the screen the mother was sat on a chair, unfastening the boy's shirt buttons and talking to him as she did so (seemed completely ordinary at this point). But after a moment or so she suddenly changed her voice to a funny, comical voice mid-speech and continued unfastening the boy's shirt and talking to him, but in a funny voice, to which the boy didn't react. Then after another few moments the mother was lifted by nothing out of her chair, hung suspended in mid-air for a few seconds still in a seated position (while screaming out still in a funny voice) and was then dropped into the pool with an enormous splash. The most bizarre thing was that absolutely no-one reacted- the swimmers at the pool didn't acknowledge a thing and even the boy didn't react- just stood staring right ahead at the chair as if the mother was still there. Even the woman herself didn't seem to be surprised that no-one was reacting. Swear to God I'm pretty sure I actually saw this for real and didn't imagine it!

As a collector of surrealist movies and TV, I am naturally curious as to what exactly this piece of TV surrealism was from and what it was all about... I was just a kid when I saw it and even then was pretty confused, but as an adult I now see just how strange it was, definitely outdoes any surrealist movies I've seen! So does anyone else have any recollection of this?