If you are in a position to hold currency in either sterling or lira then you have an interesting choice. Holding lira will mean you can access higher interests rates - say 10%. But you are also at risk of currency depreciation and if you held lira for the last 12 months it would have lost 25% of its value.
As an example, on May 7th 2013 you could have changed £10,000 into 28,000TL. If you held onto sterling last year you could change the same amount today into 35,500TL. Of course either way you would have to deal with Turkey's accelerating inflation rate but would you prefer to do that with 28k or over 35k? This choice doesn't go away simply because you never intend to leave Turkey. Thus, all you need is an excellent crystal ball that is able to tell you whether the TL is going to move up, down, or stay the same over the next 12 months.