Some good points there, Mor, thank you. Before I go further, could I ask for clarification of the Orthodox view of Anglican Communion? Is it the case that Orthodoxy considers it to be an invalid sacrament (i.e. it is not the Body and Blood of our Lord), or is it a case that Orthodoxy considers it to be a non-assured Sacrament (i.e. the Orthodox Sacrament is the Body and Blood of our Lord, but it can't be said with any certainty whether the same applies to the Anglican sacrament).
I don't think the Orthodox have ever come out with an official statement definitively ruling on this issue the way the Roman Catholics have in the past (e.g., Apostolicae Curae
). There are certain sacramental and canonical principles which apply to this question, and based on those, some will say that the Anglican Eucharist is, to use your terms, "an invalid sacrament", while others will say it is "a non-assured sacrament". But for the Orthodox, neither of these describes the Eucharist of the Church, and so I'm not sure what practical difference there is between "non-assured" and "invalid".
If an Anglican minister handed me a vessel containing Anglican Eucharist, I would treat it respectfully not because I thought there was a chance that it might be a "valid" Eucharist, but because Anglicans view it as such and if one of their ministers trusted me to guard it for some reason, I should respect them enough not to disrespect it. But I'm not holding it believing it is the Eucharist of the Church or hoping/supposing that it might be. Whatever it is, it is not ours.
edit: as a bit of a side track but would help me think through the issue, if the word "Anglican" was replaced with "Roman Catholic" in my question above, would the answer still be the same?
Pretty much, although the level of "non-assurance" among those who take the "non-assured" view is usually a little less than it is for Anglicans unless the person(s) used to be Anglican. That's just my observation from personal experience.