The culprit

I gave up. After plugging in various items and seeing the GFCI trip time and time again, I called for help. J came along, tested the outlets, "everything's fine" he said.
However, when he heard that plugging the lamp in tended to trip things, he looked at the lamp very closely, upside down even. After unpeeling the felt cover, he announced "Here's your problem it's got water in the base"
Proof came when I plugged in an electric heater which worked perfectly and is still workiing hours later.
The lamp is drying out in the sun. 
(Perhaps some of us have to be more careful with the hosepipe ;-))


Ah well...