The UK's financial system made it out battered but bruised in the 70s which were a magnitude worse than what we have right now (double digit unemployment, inflation double digit, interest rates at like 15%, an IMF bailout...). Any talk of the British financial system collapsing is as realistic as the S&P500 dropping 50% in the near future: sure it can happen but the chances are so statistically small you have a better chance of winning the lottery.