As my whole point arose because he allegedly uses 'Smith' as a cover when liasing with Kate in hotel rooms and another poster used the term 'legally' when talking about this situation and another poster didn't understand the use of that word I tried to explain it, as I understand it.
As Charles and Anne have already set the precedent of HRH Prince/ess xxx using Mountbatten-Windsor it is reasonable to assume that all of the Queen's descendents who aren't going to use the HRH Prince/ess for some reason would use Mountbatten-Windsor as a surname.
Just because he doesn't need one, in a technical sense, doesn't mean that if he does want to use one, then Mountbatten-Windsor would be the logical choice to honour a much loved grandfather.
Precedent is important when dealing with British matters and Charles and Anne have already set that precedent and that is what has to be taken into consideration as those legal documents would never have been allowed to stand had the Queen wanted to indicate otherwise. That Mountbatten-Windsor appearing on their marriage certificates speaks more loudly than anything about what the Queen intended with the LPs - that whenever any of her descendents needed a surname (and whether Charles and Anne needed one at the time of their marriages is questionable but a surname was used) then it was to be Mountbatten-Windsor.
All your convoluted arguments don't remove the precedent of Charles and Anne and on that basis my argument that, if William is going to use a surname (other than a fictional one like 'Smith') then it should be Mountbatten-Windsor.
I have found an interesting article
http://www.thestandard.com.hk/archi...=24083&sid=&con_type=1&archive_d_str=19990220 which actually supports my view. It does make sense of course that by keeping just Windsor then they are taking the mother's/grandmother's maiden name and that is only don't by children born out of wedlock so by adding the 'Mountbatten' the children are clearly from a legitimate line. This article also points out that Charles and Anne, at birth, had the surname of Mountbatten.