Re 2007 RR Sport TDV8.
The windows have been playing up for some time. It started with the 3 non-drivers windows working from their own switches but not from the driver's master switch - then, a few moments later the master would work on all 4. More recently, the driver's window stuck down. After removing the door card and switch, re-connecting the cable blocks to the switch, still nothing works but I was able to operate the windows by prodding an earthed connection into the back of one of the cable blocks.
So my question is: Do the master switches have a history of failures? I've seen them advertised everywhere, especially ebay, even on Amazon.
Any advice would be much appreciated.

Try this:

with the drivers door open, put your hand around the cable rubber boot carrying the cables between door to the car.

As you press or move it slightly does the function from the drivers switches change ?

Thanks for the tip, tried it but no go. However.....

I've dismantled the switch, not much to see - a small circuit board plus rocker switches. Re-assembled and put it back on the door. Same as before, only the front passenger window would work - and only on its own switch. Tried the others and nothing.

Then, from nowhere, everything started working - individual door switches and the driver's master.

Think I'll have to try a new switch. Ebay prices vary from £23 to £140 new, £54 second-hand. On the assumption that everything's made in China anyway, I'll try a cheap one first.