OK folks, having read all your replies, I felt confident enough to tackle servicing the fridge burner assembly (without disconnecting the gas).
But despite your suggestions, I still could not remove the bloody shield so could not clean the thermocouple. But, whilst in the pit of despair, I remembered the advice to work the fuel selection knob backwards and forwards to clean the contacts (the thermocouple output goes to the fuel selection switch).
And low and behold, the fridge lights and the galvanometer now swings firmly into the green.
We are off to the Cotswolds next week and my wife had resigned herself to not having a working fridge when off EHU. So I now I am quite a hero and have been promised a special treat tonight - lasagne with salad and a nice red.
Although I failed with the shield, I have learned how an absorption fridge works and what the thermocouple, ignitor and galvanometer look like and and how they work. So if we ever have problems when away from home I will have the confidence to tackle them - or at least understand the likely cause.
Thanks everyone (PS does anyone have some dynamite?)