Nisus people
I have sussed my mailbox issue and now realise why Inbox is not accessed with the shortcut Command One.
As in Safari shortcuts, Mail gives a number to the mailboxes in your menu. I had moved Inbox to the right; but Apple goes from left to right giving the mail boxes a number from one through to seven.
By putting inbox back on the far left, I have regained the shortcut of Command One.
Thanks to everybody. Porvadur, many thanks for Spark, Update and Desktop Utility!
Best
T