I think the UK defaults, then is absorbed into the Eurozone overnight.
I had a gentlemanly bet with my father on the subject last march, thinking it'd happen byt the end of may this year.
In August, I moved it to the end of March.
Nationalization of the banks or their failure are the two options. Once they're nationalised, it's a question of whether the world tries to hold sterling together or not.
If Sterling, including the UK govt and all those banks, goes down, then the world's financial system ends.
(My father, by the way, is a little-englander, hating anything across the channel.

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This is how bad it's got. The head of business for a national newspaper, former head of business for right-wing newspapers also... is commenting on the idea of "jubilee" from leviticus. Seriously.
Dan Roberts: The nuclear options | Comment is free | The Guardian