If anything major were to come up, it is in law that we would hold a referendum.
No, it as an act of UK parliament requiring that no further powers are transferred to the EU without a referendum.
Blimey, perhaps we should have a referendum on whether we should have referendums or not?
Seriously, do you really think the European Union Act would be any less a house of cards than Call-me-Dave' unwritten agreements? "I have in my hand a piece of paper, signed by the German Chancellor......."
Now, where have I heard that before........