When I select a calendar by right clicking and then importing holidays eM Client creates a new calendar with the holidays rather inserting the holidays into the calander I had selected! an I doing something wrong or have missed something?
the holidays are by default created in a separate calendar (in case you added them by mistake and/or wished to remove them).
If you want to import the holiday events into a specific Calendar, just go to Agenda in the Holiday calendar, Select all (Ctrl+A) and either move or copy these events into your desired calendar.
You can then remove the separate holiday celandar.