I think you generally get a better rate in Fethiye.
If you don't want to carry lots of sterling with you, you can use a Nationwide Flex account card if you have one (or have time to get one). That is free to draw cash out in Turkey.
Also I have got a Fairfx prepaid mastercard for when we go as I didn't want to have too much cash carried. If you have time you can get one through Topcashback website, who will pay you £7.50 for taking one out. You load your card with either Euro's or $ at a good exchange rate. There are no loading fees or charges for using your card in shops, restaurants but there is a 1.5 Euro charge to draw cash.
The Nationwide card does seem to be the best option but the Fairfx card is quite good as well, (better than other bank cards). I hope this is of some help to you.
Simon
