I have used a Nationwide Flexaccount for years for overseas spending using ATMs. No rip off fees and you get the Bank of England exchange rate (.which is not the rip off "tourist rate"). In the US and Canada, you will find a lot of rip off ATMs charging a fee. Use the ATMs at branches and you will avoid this con.
I use a Post Office Mastercard for purchases in currencies other than sterling. Again, just like Nationwide, they give you the Bank of England exchange rate. No loading fees, etc.
One thing to watch out for (especially in Rep. of Ireland and Spain) is companies trying to convert the bill into sterling before you sign/enter PIN to pay. This is a rip off as the exchange rate will be poor. I also have found this dodgy practice on Spanish/Irish ATMs and at the Bank of Montreal in Canada. You can demand to be billed in the local currency (euros) in Spain and Ireland both at ATMs and at credit card purchases, but I found I couldn't at Bank of Montreal ATMs. Use Scotia Bank or Royal Bank of Canada ATMs instead.
Both Post Office credit cards and Nationwide accounts/credit cards can be managed online.