Setting off this morning across Northumberland the temperature was -2 Centigrade. Initially all wipers were working but the washers were frozen solid. After a short while the rear wiper failed to wipe at all and I assumed that maybe its fuse had blown as this is not an uncommon fault if the wipers travel is restricted at all. On arriving at my destination some 1.6 hours later the rear wiper remained inoperative although it was free to move. No time to check the fuse . An hour later preparing to return home and thought I must check the wiper fuse but was surprised to see the wiper was now fully operational and the washers were also now active. Can anyone explain this? 

I’m sure the rear wiper doesn’t work if the boot is open, perhaps your boot wasn’t fully closed, or thought it wasn’t closed. I know the fronts certainly don’t operate if the bonnet is open or of the latch.

Thanks Kenny, there was no indication that the boot was open but that seems a logical explanation.