Initially downloaded the update via the MapDownloader app onto a 32Gb stick I've had for a couple of years (it 'was' the recommended minimum). Unfortunately the stick wasn't recognised. Reformatted stick to FAT32 and redownloaded update files, however still no success.
After reading the posts here and on other threads I obtained a 64 Gb SanDisk Ultra Flair USB 3 stick found at https://amzn.eu/d/9xkmVW3 (overnight delivery which was nice). As it had some SanDisk software files onboard, and having read it needs to be a 'clean' stick, I reformatted to FAT 32 and once again downloaded the update files.
Following the standard instructions I inserted the stick into one of the armrest USB slots and it was instantly recognised. After confirming that I understood the previous version would be deleted, within seconds it read a 51% upload; around 20 minutes later it had reached about 85% and then suddenly said... the upload was unsuccessful, there is no navigation software loaded and I may need to contact the dealer. Oh dear!
However, switching everything off and then having a second go, all went well.
The upload percentages went up at a steady rate until after 20 mins to much relief, the marvellous screen display of 'Map install successful' appeared
Main takeaway is the updated advice on the iGuide page - "It is recommended that downloads are done to a standard USB device, such as a memory stick (USB 3.0 is best) with 64GB of free storage space."
Thanks to everyone on this and other threads for the advice and guidance when it was most needed
