This may only be province specific: After myself and a few other colleagues have had previous emails asking us not to use the CEng postnomial before we were Licensed as PEng's. I asked around various members the reasons why and how we could appease the regulatory authority.
It seems that the CEng can be confused with the Ontario Consulting Engineer designation which requires licensing, experience and a certificate of authorisation ( see my earlier link on forms and publications).
The IET members in Canada however seem to be able to use the CEng postnomial providing there is a suffix (UK) after it, I personally have used (ECUK) Engineering Council UK and hyperlinked back to the council website so there is no confusion.
This seems to keep everybody happy or at least the members I have spoken to don't get cease and desist emails. It would be good for IET to follow up with engineering council on this issue so there is some formal recognition of the postnomial between Engineers Canada and Engineering council UK and a clear agreement of what can be accepted.
If any other members have similar stories, it would be good to hear them, especially if there is a difference in approach between Canadian provinces.