I ran out of money (dollars) once and changed £100 at a bank... no it wasn't easy and I was made to feel like I was a fraudster.

Most Americans won't have seen a Bank of England note... I think a Scottish one can be forgotton!

The method that seems to be catching on in favour of the previous way, ie a mix of travellers cheques and currency, is a pre loaded currency card like the FairFx one, which you can just use to buy stuff or a cashpoint (ATM) like you would here.