The problem has been solved. Took the car to the dealer. They contacted Honda UK who said a particular combination of radio button operations had somehow locked out the 2nd band. I took the car in and the engineer used the little trick supplied by Honda. The missing FM band is now available.
But what was the trick? And why did the engineer point blank refuse to tell me what it is? What happens if, sometime in the future, the same thing happens again? And the car is out of warranty?
What will the application of this little trick cost me?
I think all that was done was to return the radio to the factory default status. How was that done?
Perhaps disconnect the power to the radio and then reactivate it with the secret PIN supplied with the radio. Does anyone have any suggestions? Any radio experts who'd like to enlighten us?