The rubber cover on the switch for the tailgate had totally melted and turned into tar, no idea why as this happened in the UK before leaving for France plus I owned one in California.
I managed to find a replacement on Amazon for about €20, much cheaper than a new switch assembly for which I was quoted £55 plus shipping. Getting the old switch off was a PITA, one screw would not turn and the angle for the screwdriver is impossible for any sort of power tool. I had to resort to removing all the interior trim from the tailgate, then removed the chrome bar which has the switch in it. Then I had to drill out the bad screw and start cleaning all the mess - took ages of soaking in petrol and stiff brushing after totally dismantling the switch.
Eventually all was reassembled and remounted after about three hours of work.
So, if yours has done the same thing, save yourself a ton of aggro and buy the new switch!