Thanks for your reply. Much appreciated. I did all you suggest many times. The Gemini (mount) never connects. I have tried it on its own with nothing else connected. ls -l /dev/tty* then shows no port suffixed by USB. Plugging my mount into either a Pi USB 2 or USB 3 port immediately generated a ttyUSB0 port. It never connects to KStars. The error message is always the same " [WARNING] Port /dev/ttyUSB0 is already used by another driver or process."
In all honesty, I would not have written had I not been totally stuck. Finally, plugging my mount's USB cable into a Windows 10 laptop it immediately connects to Stellarium either via Stellarium native or using the ASCOM driver.