To be on the safe side I'd recommend you take some lira to tide you over for a day or two and take the majority of your spending money in sterling travellers cheques. You can then change the cheques at a bank.
Last year we went to Turkey for a day trip on the spur of the moment (from our holiday in Rhodes). We didn't have time to buy any lira which is how I know they will take euros and sterling cash. I've been to Turkey 6 times in total and love the place.
Where exactly are you going?
i'ts a pity they dont take their own turkish currency , given that sterling is strong against it , and you would get more when you changed sterling for their currency - if you see what i'm trying to say .
turkish lira
but everything is priced in pounds there and they are happier to take pounds rather than the turkish lira.
i staye din marmaris and found it very nice .have a goood time there.