Hi Mark
I usually take a mixture - enough Turkish lira to see you through the first day (as you'll get a better exchange rate over there), some sterling and sterling travellers cheques. Travellers cheques can be cashed anywhere, you don't need to visit a bank or change office. I always use the supermarket under the
ICR office to change cash and cheques and you get the same exchange rate for both (just write your passport number on the reverse of cheques before handing them over - they may want to see your passport the first time you cash though, I don't have a problem with this as they know me quite well in there!

)
Just make sure you hire a safe box at your accommodation for the duration of your stay - they're normally £10 a week.
Hope you have a great time
Mazz