Thanks for the reply and suggestion Steve, much appreciated... But, no I don't think this is related (but could be wrong). From Wikipedia: "a media access control address (MAC address) of a computer is a unique identifier assigned to network interfaces for communications". So our Mazda 6 have one for the Wifi, and one for the Bluetooth. Knowing your MAC address allows you to define a list of "authorised" devices (computers/mobiles/cars) for access to your home network, portable 4G modems, mobile hotspot, etc.
Seems the simplest approach will be to turn off MAC address filtering, connect the car, read the MAC from the router, then add it to the whitelist, re-enable MAC filtering, etc. etc. A bit silly something as trivial is not available from the network settings interface.