Do not exchange your money in the UK. No matter where for how much, you will lose money. The exchange rates in the UK and in general all over Europe, especially at the Airports are ridiculously low.
So, bring your currency over to Turkey, for two well good reasons;
You can shop with your Currency, whether it is Sterling, Euro or Dollar, without any problem whatsoever.
Secondly, if you wish to exchange your currency into Turkish Liras, be assured that the exchange rates over here are very high. Also, you won’t have any problem to find a shop that is willing to exchange it for you. In Sarigerme, everyone will be happy to exchange your currency into Turkish Liras, this includes Clothing shops, Supermarkets, Pharmacist, Jewellery Shops even the greengrocery in Sarigerme will do this.
British Sterling is floating around 10 Turkish Lira, Euro about 9 Turkish Lira these days. (21.February.2021) This page will be updated when there is a dramatic change in the currency.