Thank you for all these ideas, I did clean the switch but will go back and try again. I will check earths where I can and at some point, if I can't get it working any other way, may well try to remove the bottle and turn the motor, but I think it may have to wait until after we have been away. My biggest fear is that I undo things and then can't redo them, leaving the van unusable and my OH's two weeks holiday off, ruined. We've just managed to get the van in order after much work on the cooling system, which now seems not to be leaking, losing or using water etc.
I am hoping my garage might have five minutes to test the switch later today, Oldie has suggested I get a multimeter, which again might be something for me to learn in the future, but again, time is limited.
I have grass to cut now, before it gets too hot....we have lots of grass, then I might have another play until I phone the garage after lunch.
In the meantime, I've dug out a wicked spray bottle......
Thanks again for all your ideas, advice and likeminded tales of screen washer woes. It's good to know I'm not alone