Thanks all! I couldn't follow your steps AG Falco as there is no 'Menu' button on my headunit - it's exactly what I have been struggling with watching all tutorials; I'm unsure whether mine is a new version of the headunit (as the car is late 2019), but there are only 3x buttons on each side (see photo) whereas all tutorials have 4, including a physical 'Menu' button where you can select Android Auto from. Anyway, will leave this as a legacy post for any future people struggling as I have eventually found the answer - Steevs I followed your steps and still no Android Auto was appearing on the screen, in truth at that stage I got a little frustrated and ended up tapping everywhere on the screen - much to my amazement you have to touch the Android Auto logo (see photo) after pressing the 'app' physical button, and voila - Android Auto connects and the user interface changes ....
Feel pretty stupid, but I would argue it's not clear at all that you have to touch the unassuming AA logo, particularly when an iPhone connects automatically on plugging in the USB.
Anway, thanks for the help guys - all works fine now.