I downloaded the NaviExtra's app to my PC and it seemed I was entitled to a map update so followed the instructions, I did the update today, the guide says not to unplug or turn off the car during the update, the first screen showed as 'Checking Files' but screen went dead after a short time. I used Jto's advice of two pushes on brake pedal and tried again 'Checking files.....' went dead, restarted and I noticed checking bar was progressing so just restarted when needed.
Eventually the screen advised 'update successful' Phew!
Checked the MG Touch Navigation screen, that was exactly the same and seems not have updated anything! Is there a way to check it?