O ne of the practical obstacles faced by the campaign for a second referendum on leaving the EU is the view that it cannot be held before the planned Brexit date of 29 March. That means that if the UK is to hold another referendum, it will have to apply to extend the Article 50 deadline.

But why does it take so long to hold a new referendum? Why did the Constitution Unit at UCL estimate that it would take six months? Surely the process could be speeded up in what is, after all, a national emergency?