This is the current structure for the various European Bodies. It is now recognised that the Eurozone requires a banking union. I think it is also clear that the UK will not be part of this. It may be that the Eurozone moves further, but the situation is so volatile at the moment that it cannot be clear. What should, however, be clear is that the UK should not aim to be part of the core Eurozone countries.
If there were to be such a proposal then the law now is that the UK would have to hold a referendum.
My own view is that there will become a time when there is merit in having a referendum as to what the relationship should be between the UK and other European Countries. There will only be a limited range.
I don't think there is anyone suggesting that we should not be part of the Council of Europe. It is, however, the membership of the Council of Europe which leads to us being part of the jurisdiction of the European Court of Human Rights. Much of the criticism of the ECtHR is unfair. However, it is clear that it should be accountable to special resolutions of the Parliamentary Assembly of the Council of Europe. That would resolve the issue of the remoteness of ECtHR. If the UK were not part of this jurisdiction then one would expect it would fall to be part of the jurisdiction of the United Nations Committees on Human Rights. Here are more details about the UN bodies to which there is an individual right of petition.
We then have the EEA. The EEA is governed by the rules of the EU, but is not part of the CAP or CFP. The EEA gives the rights of free movement within the countries of the EEA. This is another issue about which there is some stress.
Then is the EU itself. My own view is that given that we would not wish to leave the EEA it is better to take part in deciding what the rules of the EEA are. Hence I think being part of the decision-making body is best.
At the point at which it becomes clear what the future bodies in Europe will look like (which is not clear today) then there is a good argument for a referendum as to where the UK should rest within this. It is quite likely that this will happen within this parliament, but it has not happened yet.
The difficult question is that as to what the question should be. Do we have a range of options including leaving the Council of Europe or do we have a more limited range of options? Should we have the option of joining the nucleus of Europe or not?