Thanks for all your help. I've no idea what has changed, but using the same leads and the same Apple phone as earlier on in the week and everything is working now! I can connect the phone using the USB lead and it charges. When plugged in to the USB, Google maps prompts are broadcast over the car radio speakers, and Spotify works in a similar way. When disconnecting the lead, sound is lost confirming that the USB is performing the sound connection (as you would expect). Switching to the Bluetooth connection from the media interface on teh radio then reconnects the phone via Bluetooth