iPhone6 and Macbook Pro USB personal hotspot not working

I have a 2015 Macbook Pro running OS X 10.10.5 and an iPhone6 running iOS 9.0.2.

When I plug in the USB cable, iTunes launches and recognises the iPhone but the MBP network does not see the iPhone and refuses to use it for internet access. When I switch to Bluetooth, everything works, so this is a USB problem of some sort.

I have resent the iPhone network settings and I have rebooted both devices, but this doesn't fix it.

Any help gratefully appreciated!