The simple answer is that running as root indeed works, thanks for the tip.
What I still don't understand is why. Follwoing the README instructions I set permissions to allow everyone (chmod 777) for /dev/bus/usb and recursively to all the directory tree below it. This should have allowed the permission to talk to the brick from any user, so what have I mimssed?
Doing lsusb -v as a regular user I get:
Bus 004 Device 003: ID 0694:0002 Lego Group
with lots of other details and some that are not accessible to a normal user appearing as not allowed.