Some interesting points in this thread.
I must confess it is a while since I read CAP 413 but rather than "Confirm Cleared Flight Level" should it not be "Verify Cleared FL"?
As commander sometimes one is not in complete control of the R/T! I have had a couple of occasions fairly recently where my colleague has asked (without reference to me!) "Do you still require us on this heading?" and also "Are there any level restrictions at XXX today?" - one doesn't want to spoil the decorum on the flight deck but not consulting with the commander before making superfluous R/T calls is also one of my pet hates, notwithstanding CRM!