Thanks Noel and Simon for the replies.

All the metronome options are set correctly as they have been for years and I am using version 1128 however I may have solved the problem without understanding why.
There is an option under Song/Action Menu/Options that for some reason I had set to "Play When Chosen" This isn't the way I want it so I deselected the option and now the metronome works again - go figure!
I have learned over 25 faithful years with BIAB never to count my chickens so I have my fingers crossed.

Tony