Dear John Francis,
Yes, let me agree with John that there are no substantial doctrinal differences between Orthodox Churches, but there are differences of culture. Indeed this is why the British Orthodox Church exists as part of the ancient Coptic Orthodox Patriarchate, rather than our communities simply being part of the Coptic Orthodox Church.
We have been given the mission of helping people to live out the fullness of the Orthodox Faith in our own British culture, not that we exalt being British above being Egyptian, or Greek, or Russian, but that the Orthodox Faith is for all peoples in all places.
So where there are differences they are generally cultural rather than doctrinal.
Take the issue of language for instance. There are often controversies in the Orthodox Churches when they find themselves in an Anglo-phone context and need to grapple with the choice of language in worship. in my own home town there is a Greek community, but it worships almost entirely in Greek, and though I could probably learn enough Greek to participate in time, it would be very hard for my family, and even harder for any non-Christians who might want to discover Orthodoxy for themselves.
But the Coptic Orthodox Patriarchate, which also has to deal with the issue of language, has wisely understood that as British people who are Orthodox it is natural, and appropriate, for us to use English in our worship.
It is also natural and proper for us to venerate the saints of the British Isles, together with those of our Mother Church. We also keep the Western calendar, apart from the Paschal cycle, because in the UK Christmas is kept on the 25th December, and we are British.
These are the sort of things where there are differences between the British Orthodox and other Orthodox.
There are also a variety of cultural and social customs and taboos which have meaning in rural Greece, Russia or Egypt but which are not part of the Orthodox Faith and therefore do not need to be reproduced by British Orthodox. These include some attitudes towards women, but also minority groups like Jews.
I hope this is a little helpful