"If remaining in the EU was certain to lead to the break up of UK, either into its constituent countries, or by EU recommended regionalisation, would you favour Brexit to protect the integrity of the UK?"

Fair enough, I'll have a go. I don't think it quite comparable, though, because we have been in the EU for a long time and the country has not broken up, whereas the status of NI in particular is a huge problem for Brexit.

When it comes down to it, in extremis, I have NO loyalty to speak of to the UK. I would not call myself patriotic. I haven't checked but I imagine 'patriotic' is derived from 'pater' and I recognise no abstract father that is the country. So I would stay in Europe.

Feel free to skip all the following, because the essential point is above, but this is to elaborate it.

I have little or no affinity to "King and Country". Growing up in Middlesbrough, my identity was 'Yorkshire' and that was far more relevant than anything else. In 1968 we were moved by political whim out of Yorkshire into Teesside with the full understanding that in a few years time - 1974 as it turned out - we would be moved again, this time into Cleveland. Now it would be absurd to suggest that was in any way formative, but it did make me more aware of the arbitrariness of regional labels. There is plenty about the UK I like a great deal, including a tolerance for others that, for its many shortcomings, is still better than many other countries. Through simply living in it I am adapted to the UK to such an extent that living anywhere else would be difficult. But, "in extremis", there are many other parts of the world I could move to with little regret. That includes virtually everywhere in Europe but also a good many other places.

So I have little allegiance to my nation state. What I do see is that issues - for the sake of generic term - need to be addressed at an appropriate level. If you are bothered by litter, you need to be hassling the local council, not the national government or the EU. Climate change, on the other hand, needs to be addressed at a level higher than even groups of states like the EU. I also see that over the last hundred years or so multinationals have outstripped the control of individual governments. All this stuff about the big companies avoiding tax and so on is real and it arises because it is beyond the control of any individual country. When a country says it cannot tax a business because they would move elsewhere, it is acknowledging its lack of sovereignty over that company.   The control of such companies is arguably growing beyond the control of groups of countries like the EU, but it is well beyond any individual one. All the cries of 'sovereignty' miss the fact that so much of our life is decided by multinational companies. The EU is one multinational deciding things: it is one out of dozens - and just about the only one we have direct influence over.

In that context there are issues that need to be addressed at the local level, others at the national, others at the international and others at the global level. My support for my nation state is really that it just another level at which it is suitable to address some issues. I have no loyalty to a country: I have a desire that problems are solved and the country is an appropriate level for some of them.

So getting back to the question more directly: Losing the UK as a group would be losing one such level, and I would oppose it. But not at the cost of losing levels I regard as more important.