Thank you Charlie. Yes it has been a funny season!
My main point of confusion was the strong budding as Spring arrived (finally) and then the sudden loss of them all and the current awful looking state of it.
I have other viburnum, various types in the garden too, all very close to each other, so I will need to be very watchful of other damage. Funnily enough, early last year, I had an Escallonia (many years old) which mysteriously just packed up and died on me, had to cut and dig it out. Other shrubs, including a viburnum 'cane'/sucker I took from the now 'dying?' one I've described here, a camelia and euonymous are growing very well in the huge gap it left!

Cheers

Terry