Dear Mahmoud,
I think that being a dual national as in British-Egyptian then you are exempt from military service, voting and self-nomination for elections.
The problem is however that if you don't notify the authorities that you are a dual national then you are not legible of holding the Egyptian citizenship and they just cancel your citizenship. Bunch of over-proud snobs aren't we?
The best thing to do is to ask the Egyptian consulate coz the probably have the best answer.
Good luck.