Hello Tony,
Thank you for taking the trouble to answer.
I am afraid I have more questions... Yes the radio connects via the wifi rather than by a physical cable into the back of the Hub from the device but I do not understand about splitting the wifi bands and turning off smart wifi. My husband has checked that we have the latest firmware on the device.
I upgraded to a Hub4 because I was invited to do by Virgin Media and it seemed like a good idea at the time. We still have the old router but in the light of what you say about how difficult it might be to revert, I will probably not attempt to do this but return the old one as directed by Virgin Media, within the next few days, and to be fair, the old router didn't always manage to keep the radio playing either!
So long story short I'm not really any further forward with this. But thanks anyway!