...a two-thirds referendum majority in such an important matter. That way you can be assured that people generally are in favour of a change from the status quo.
The trouble with that is when 35% vote "Remain" and 65% vote "Leave", and the government says "Nope, less than ⅔, so not a big enough majority". That way lies violent revolution, unfortunately. Or at least downfall for the government & election of UKIP. On the other hand, it would definitively put paid to Scottish independence.