Here is the letter from the Scottish First Minister in full:
I said on Tuesday that I would be publishing the detailed democratic case for the transfer of power from Westminster to the Scottish Parliament, now being sought by the Scottish Government, by order under section 30 of the Scotland Act or an Act of the UK Parliament, to allow for an independence referendum that is beyond legal challenge.
I am enclosing a copy of that document.
When we spoke on Friday, you reiterated your Government's position on this issue - however, you also committed to engaging seriously with our proposals.
Indeed, I believe that on this - as on any issue - you have a duty to do so in a considered and reasonable manner.
I therefore look forward to discussing matters further with you in the new year.
In the meantime, please accept my best wishes for the festive season.