Thank you for your response.
I must disagree with you reference changing the status quo on a close vote. No vote was held prior to the UK joining the EEC, although a confirmation vote was held later. Several EEC/ EU votes have been very close over the years and treaties implemented on the simple majority basis of those votes. For example, the 1992 Maastricht Treaty was implemented by France based on 51% in favour, and by Denmark on the second attempt, after it was firstly rejected, by just under 57%. Many governments, including in the UK, decided not to offer their citizens a say. One can only speculate why, however, this was an example of a fundamental change in which a majority was not required as the people weren’t consulted. A little later Sweden joined the EU based on a 1994 vote of just over 52% in favour.
If you believe a significant proportion is required in favour of changing the status quo, perhaps 66%, then it is likely several treaties would not have been accepted including Maastricht, Amsterdam and Nice. Additionally, several countries would not have met the target and would not be EU member states. I also do not recall many referendums held about joining the Euro, a fundamental change, and of the 2 that were held both would have failed based on the closeness of the result.