Many thanks to you all for your contributions, I've stored them all for future reference, however, jimjim1, you are spot on!
Having settled down with mug of coffee to launch myself into the intricacies of the bowels of Windows10 I had a quick look at System Update … all was well, it had fixed itself!! I've no idea how or why but things appear to be back to normal.
Once again, many thanks to you all, FZ