After MUCH messing about I got it connected. I tried 2 desktops, 2 modem/routers, 3 cables, an iPad and a temporarily wired laptop, Windows 7 and 8.1(X2).

The final clue was the white/orange blinking power LED. I suspected it was in firmware update mode and it WAS (or whatever?).

Somehow it was stuck in firmware update mode!? It kept saying the 'net wasn't there and the ethernet cable was not connected and other misleading errors....

Did a "Factory Reset" on the router and the Genie came up in the browser. From there it was plain sailing.

Just in case anyone else hits the same symptoms