Actually you can - you need a notary solicitor in the UK (check you local practice as they should be able to do it). For use in Turkey it also needs to be sent to the (UK) Foreign Office to receive what is known as an apostille stamp which legalises the document. Then it is returned to the solicitor, then can be forwarded/taken to Turkey for use.
All that said, I have also had power of attorneys sent from the UK that were nothing more than a few lines of handwriting on an A4 sheet, signed at the bottom, and I was allowed to use them in the Turkish offices of power. Here (there) is Turkey, as they say...