Thanks for some more replies, much appreciated again 
. It does seem like Alex tends to be the go to nn (in England/Wales at least, which is what I'd guessed) but that I could probably push for another nn if I introduced it from day one/that's what he wanted himself at school. Really interesting to see a couple of you know a Xan!
In your situation if his name is causing so much angst do you think you might not be better off using a different one?
I completely see your point but my problem is I seem to have a naturally very classic/timeless naming style and many of them have been used already in my large family (George, Henry, Jacob, Mark, John/Jack, Robert, Thomas, Frederick, Peter, Joseph, Benjamin, James, Theodore, Owen, Daniel, Luke, Christopher...) and some of the ones that haven't, I'm not sure they sound great with my surname.
....Or I'm being a fussy so and so like with Alexander and like the full version but not the most common nickname eg. Edward (don't like Ed/Eddie/Teddy, prefer Ned), Nathaniel (don't like Nate, prefer Han), Matthew (don't like Matt). I'm awkward, I know! 