Dear Help,
I am not a lawyer but a destination wedding planner and I have been helping foreign couples get married in Turkey for 5 years. I have done Iranian and British weddings before but it was the girl who was Iranian and the guy was British, however, the procedure is pretty much the same. Your partner will have to apply for a no impediment certificate from her local registrar and bring this, her birth certificate, passport and any other document which would be applicable, such as a decree absolute, to the nearest British Consulate where you are hoping to get married. You will need to obtain a similar document from Iran, to prove that you are free to marry, and take this, along with your birth certificate and passport to the Iranian Consulate in Istanbul. Both consulates will issue the paperwork that needs to be handed in to the registrar who will marry you. Please note that these documents will have to be authorised at the local Governor's Office first, before you take them to the registrar.
Although you are not marrying a Turkish citizen, you will still be getting married according yo the Turkish civil law, there is a seperate section defining the procedure for two foreigners getting married in Turkey.
Best of luck!
Hayal