Thanks all. Have got motors running. As suggested I did a "CSC" (what does that stand for?) All OK.
Colin at DJI USA didn't show that bit on the video - hence I was expecting the motors to start out of the box, like his did. Mine didn't!
As for the CSC method in the Phantom Quick Start Manual 1.6, you have to work your way to p.13 (Flight Test) before you hit the CSC stuff. Not a smart placement, in my opinion, as all I wanted to test is whether the motors (no props attached) could actually be controlled by the Tx.
Such a test is not "Flight Test". I classify it as: "Check that your Tx communicates with the motors on your aircraft". A pretty basic test, I think. I get a complex bit of gear out of a box from China. I plainly am wondering: does this gadget do what it's supposed to, or do I have a dud?
Better invent a new category, perhaps called "Preflight Check" Place it at the the beginning of the manual. Oh dear, writing manuals is not easy. Particularly for people already in the know.