Sorry, your wrong.
If you use UK debit cards (Cirrus, Maestro, Switch) etc in a foreign ATM you will generally not get the interbank rate and may pay commission charges. If you use credit cards you will normally lose 2.25 - 2.75% in exchange rate and commission charges. If you use UK bureaux de change you will lose your shirt.
Because my foreign expenses were quite high (£2 - 3,000 per month) I researched this quite carefully.
If you use a Nationwide debit card for cash and credit card for other payments you will get interbank exchange rates on both and will only pay commission if the foreign bank levies a charge. So far as I can tell, they are the only card provider in the UK who do this.
In the last two years I have done this in Holland, Sweden, Switzerland, Hngary, Germany, France, Denmark, Italy, United States, Egypt and Nigeria and have only paid commission ($1.50 to the foreign bank) in the US. Whenever I have checked, the billed cost of each transactions was within pennies of Financial Times interbank exchange cross rates.