The entre global banking system is unstable since there are massive currency dependencies between countries and between banks. A country’s boarders pretty much have no bearing on these interdependencies. What is more, it is not just about loans going bad, but derivatives. We have not seen these in the press for quite a while, but there is far more that is creating this instability than just a few small European countries going belly up.
The UK is no longer viable – the government is spending far more each year than it takes in in the form of taxes.
So although we could see the collapse of the Euro, it would no doubt take Sterling with it.
And don’t forget that with fiat currencies, they have no intrinsic value – money nowadays is basically debt, and central banks create far less new money than commercial banks which can lend out the same deposit many times over.