UK is not using Euro, so the banking/payment system won't be affected by brexit.
And after brexit, UK can always sign free-trade deals with EU, just like NAFTA btw US, Canada, and Mexico.
The only thing brexit will help achieve is to prevent refugees from entering UK too easily. so why it is such a big deal?
the big concern is EU dismiss at end while other countries follow BR.
once they played it before the event, there should be no bigger bad surprise after, let's see