I started to strip out the tailgate side trim where the relay is located and then remembered that I needed to remove the bottom trim under the tailgate door before I could remove the panel.
As it was absolutely chucking it down prior to snow arriving later, I thought sod it, and checked all the cables inside the tailgate door as best I could. I found the connector to the regulator and gave it a good wiggle.
I was about to go in for a cup of tea when I thought why not try the switch and listen for the relay clicking.
So, I started it up and whilst squeezed in the boot area, I pressed the console button and I heard the click of the relay. I then realised I could hear more than just a click and noticed the metal frame holding the rear glass moving slightly as I jabbed at the button. I took the tape off that I used to keep the rain out and tried the switch again. The window came down fully, then I brought it fully back up. The rear wiper is now working again, so is the rear window heater.
So, I am guessing that the connector to the regulator was not fully making contact. When the rain stops I will unplug the connector and give it a good clean with switch cleaner and then some WD40.
I just hope this lasts. I didn't fancy having to drive it in the snow we are expecting with no rear wiper and no rear heated windscreen.
I then went indoors and there was a knock at the door. It was my replacement relay!
Assuming all keeps working well, a big thank you to all on here as usual for your suggestions and help. Much appreciated.