As Obie said, you will be free to
marry with a diplomatic passport (without your parents'
consent if you are 18 ore over). The marriage registrar will only look at it for identification purposes.
Moreover, there is also no requirement for you to apply for any
residence cards under the
EEA regulations. However, I don't think there would be anything to prevent the UKBA from endorsing your diplomatic passport appropriately, if you cease to have
diplomatic exemption.
I'm not sure if the act of marriage is sufficient for you to
cease having diplomatic exemption, under the
Vienna Convention on Diplomatic Relations. Your country or your father may have to waive (
Article 32) your diplomatic rights (
Article 37). Your father will know.
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