I've continued to muse on this topic, because it raises such deep questions in me. So three more or less related points.
1. I have no doubt that, eg in the context of Roman persecution in the early church, or in the context of the oppressed Chinese churches of recent memory, there have been celebrations of communion without a canonically ordained priest present, where Christ was fully present in whatever way you want to understand that to be, and where the activity was as meaningful as it could be. In a related fashion, I don't have any problems with a house group sharing communion amongst themselves, for example (though that depends a little on how it is understood). The issue, for me, is when that form is chosen exclusively over against a possible alternative, viz having an ordained person presiding, because of what then seems to be rejected: the reality of the wider Body. What I most struggle with, in the extremes of Christianity (ie at both evangelical and Roman Catholic ends of the Western spectrum), is the idea that 'unless you're exactly like us then you're not a Christian'. To my mind embracing the authority of an ordained priest, ie ordained by the wider church, is precisely about saying 'this is bigger than us', 'we are not the centre of gravity' and so on. It's about Christ not being the possession of the small group. I'm still digging into this perception of mine though; sometimes surprising things have happened once I uncover the roots of something like this. I am not yet fully clear on what I'm being led to understand about it.
2. A specific point: much of the advocacy for lay presidency talks about the Passover ritual, which didn't require any form of ordained ministry to be carried out (though I believe it was still 'presided over' by the head of each household). This seems to only draw on part of the roots of communion, for an equally substantial origin for communion is the Temple liturgy (Jn 2.19-20), which had the most extreme elevation of ordained hierarchy possible. A large part of the language that we use in Christian theology - eg Son of God language - stems from the Temple liturgy, so it can't just be brushed off.
3. I had a very specific vocation experience, that was centred on the notion of presiding at communion, ie that was literally the vision I was given. It was not at all a welcome vision and I fought against it. Yet I couldn't deny that presiding at communion was precisely what I was called to do. When I attended my selection conference I was pressed on how I understood this by a Bishop, and he exhumed the fact that my understanding was still quite shallow. He directed me to read this document, wherein the Church of England set out a) it's understanding of communion; b) the role of the president in communion (indissolubly linked to overall responsibility for a community); and c) its rejection of lay presidency. It was b) that I hadn't fully absorbed - and which I'm still wrestling with - but c) can't be separated from a) and b). So this question raises the profoundest possible question about who I am called to be by God. Put differently, if lay presidency is accepted then I no longer know who I am called to be - I don't know what the point of my life is. One of the key challenges made to me when I first began exploring ordination was 'what can you do as a priest which you can't do as a committed Christian?', to which the answer is 'preside at communion' - but not simply as that act, but all which that act represents in terms of b) above, ie to bear responsibility for shepherding and feeding a flock. It is that which is my vocation, and presiding at communion is the necessary sign of that vocation. To separate out that general authority from the action which expresses its meaning is to unmake the vocation itself; all that seemed solid melts into the air. I'm afraid I can't get away from seeing that rejection as either a rejection of sacramental theology as such (because if the sacraments have no incarnational reality then the role of the president is deferrable and delegatable) or simply - as I said before - an issue about rejecting authority, which, leaving aside my cheap cracks about adolescence, is profoundly unScriptural. Either way, I must confess that my vocational experience is an unarguable reality in my life - subject to further direct revelation of course! - and it is deeper in me than my attachment to the Church of England. If the Church of England changes it's mind and accepts lay presidency then I would undoubtedly leave this Church. I doubt I'd be on my own in that.
Ho hum. I'm sure I'll continue to gnaw on this bone.