As you are in UK you will have to get your power of attorney drawn up, translated into Turkish and notorised and then take it to the Turkish Consulate in London followed by the Foreign Office near Marble Arch to have it validated before sending to your agent in Turkey (I sent by DHL). When I did this the agent provided the form of words ( which I checked to ensure that they were specific) which I took to my solicitor.
You may find this site useful but its a bit legalise
[urlhttp://www.tbcci.org/power_of_attorney.php][/url]