The definition of major is completely subjective. Adopting the Euro if the UK remained is major. What was a ‘major’ change when leaving? Everything has been mitigated by slow change. Euro migration was overnight in 1999 (I worked on it) that was major. And if that went to a referendum should be 60-40? What happens if it were 59.9-40.1 ?

Obviously majorness is a matter of degree. And, yes, different people can weight things differently when deciding what's major. But you can't escape having to decide that sort of thing -- after all, you can't hold referenda on everything and so you have to decide what things are "major" enough to need a referendum.

(I am inclined to think that most things major enough to need a referendum are also major enough that if there's a "change" and a "don't change" option the latter should need some kind of supermajority.)

> And if that went to a referendum should be 60-40? What happens if it were 59.9-40.1 ?

If it was set up with a 60-40 threshold then 59.9-40.1 means no change, just as if it was set up 50-50 then 49.9-50.1 means no change. I'm not sure what the problem's supposed to be here.