Success … sort of.
Removing "BatchMode yes” from the backuppc users .ssh/config file fixed everything EXCEPT
the backuppc user still could not ssh out from the backup computer (sirius) to other computers.
However, the error message was now a lot clearer (complaining that login not allowed because the account was locked).
All of the client computers have a backuppc user with the shell set to /bin/false (the recommended procedure) as there is no shell login required on these computers.
However, changing this to /bin/bash solved the problem … backuppc user can now ssh from the backup computer (sirius) to others.
Any ideas as to what may be causing this last issue ?
PS UsePam is set to yes