The 3502 Manfrotto COMPACT LEVELING HEAD is a very handy extra for a lot of tripods that don't have a central bowl. I used to use one in conjunction with with one of my older large Manfrotto studio tripods and heavy MK2 head.

The effect is "perspective". When exagerated by the tilt of the camera sensor it's often referred to as "keystoning".

Go stand a mile from a skscraper - the left and right sides look parellel.

now go stand by the skyscraper and look up - it converges towards the top.

You cannot adjust your tripod to make the "known vertical lines" parallel with one another.

Not applicable in my scenario. I was shooting in a sports hall, nice flat floor, square room etc. The camera, initially hand held, was pointed directly at the wall ahead 90 degrees to it. it wasn't the vertical line that went out, it was the horizontal where the dark floor met the white wall it clearly went 'uphill' to the right.

When I later came back to re-shoot with a tripod, getting it all level I noticed in the LCD screen that the HORIZONTAL line of the floor had a small incline to the left. When I then downloaded the video into my editing software it was in fact level, thus suggesting the image - in the LCD - is not set correctly

It has nothing to do with skyscrapers or vertical lines - that is just an example. Perspective applies everywhere. Stand far left in front of a really long stage. Now point your camera at the center of the stage. The stage will appear to tilt away from the camera. The front edge of the stage will not be parallel with the bottom of the viewfinder.

This is not an optical aberration - the effect is apparent to the eye - but the eyes FoV doesn't have a defined lower edge to make it so obvious.

The suggestion that the LCD in this camera is distorting the image in the way you describe is extremely unlikely and very easy to check.

Yeah, like I said, I went back re-shot the scene on a tripod that was level and 90 degree to the wall, the floor line looked like it was going up hill on the LCD but fine in the editing software - thus LCD at fault but I learn to live with it