After an afternoon was spent jiggling with switches and getting nowhere fast, I went for the back to basics approach and took the door apart. Many thanks to all for the suggestions.
The window was making the 'shut off' noise when it reached the end of its travel, which occurred about 1/2 a second after pressing down on either the driver's door control or the rear passenger door control. I heard nothing when pressing UP. I was convinced that it wasn't the switch as I was getting the same result via either of my 3 methods.
First port of call was the multi-plug connector for the motor, and my first touch of the plug made the window jolt upwards. I started to yank the plug off to inspect the terminals and to my surprise, it came out very easily despite having two shoulder tabs which should in theory retain it firmly in the socket. All electrical connections were as clean as a whistle. I put the multi-plug connector back in the socket on the electric window motor and heard a satisfying click and then thought Arrrrrgh. I'd quite simply not pushed the smelly thing home hard enough for it to latch when the top half door assembly was changed (by myself, I hasten to add) about a year ago.
I suppose that over time, the connection had become loose enough so that only the window down functionality worked. And they say a bad workman always blames his tools.
Today, I am that bad workman!
Lesson learned
