There seems to be a scare about the Nationwide card every year on CBF.
I have checked and as far as I can see we will still be able to use
our card without charges when we are in Turkey.
Reference the Santander card, we have one of those too.
The card can be used to buy abroad with no penalties, it's the
same as buying in the U.K. So if you pay the card in full at the end of
the month you incur no extra charges.
We got one to use in the States last year, it was great, no problems.
Also in the States they don't ask for your pin number, you just
sign an electronic keypad.