Why is a comment by Salmond binding when a Vow wasn’t?

Source::
The National
Why is a comment by Salmond binding when a Vow wasn’t?

ONCE again a Tory PM makes a once-in-their-lifetime visit to Scotland and trots out the meaningless mantra that the 2014 referendum was a once-in-a-generation event, more binding and sacred than the Ten Commandments, to effectively deny a democratic imperative and mask his utter contempt for the Scottish people.

Read the full article::
The National
Why is a comment by Salmond binding when a Vow wasn’t?