According to the law, the constitution and the parliamentary debate that enabled it, the EU referendum was not a decision, however the EU Notification of Withdrawal Bill was passed on the basis of 'A decision already made.' The government should set out who made that decision & the reasons for it.
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Future historians will look back on this period and ask how such a seismic constitutional shift came to pass.
The record has a significant gap.
What was set up by parliament as an advisory referendum appears to have become a decision without any parliamentary process to make it so.
The only known document relating to it is the government's pamphlet.
The government needs to either identify who made the decision and set out the reasons for that decision, or explain how the referendum became a decision.