I am humbled by both the quantity and quality of responses so far - whether supportive or not, whether I agree or not, they are uniformly of a very high standard, and are each in their own way helpful - thanks to all.

As a (minor) aside to this story, I just spoke to my wife. She is eligible for UK citizenship, but has always refused to take it up because she'd have to renounce her Chinese citizenship, which she was reluctant to do for reasons of identity, and inheritance (foreigners cannot own property in China). I just told her that she has to have a UK passport now, as we can't have this happen again - and she, in good humour, agreed!

So pleasingly I can eliminate this kind of risk entirely from my family's life in due course!