"Misery acquaints a man with strange bedfellows," says Trinculo as he dives for shelter in The Tempest. In the theatre, you never know who you might be sitting next to. Especially at a first night, and especially if you are stuck in the middle of a row.

You can be lucky, though. Last Friday I was sitting next to a little bird-like lady in the Theatre Royal, Norwich, who introduced herself as the mother of actor Adrian Schiller, who opened last night in The Captain of Kopenick at the National. I looked out for her in the Olivier to say hello again - she'd told me she'd be there - but no luck.

My own guest had cried off and my second ticket had been taken by a perfectly pleasant chap who kept himself to himself until the curtain calls, when he said something interesting about the play and we bade each other goodnight as if we'd been friends for a fortnight.

The couple in front had no such inhibitions. They were talking, canoodling, even eating, throughout the performance, but I think they'd arrived already semi-acquainted. I was on tenterhooks anyway, as I've had a terrible cough for a few days and was stoking it with ju-jubes and water sips throughout; you know that terrifying moment when your throat starts tickling and you never know whether it will quieten down or erupt in a hacking clamour. 

The night before, at the St James Theatre for Our Country's Good, I found myself sitting next to Neil Kinnock, the former Labour Party leader, now Baron Kinnock, and his wife Glenys. We exchanged minimal pleasantries but could find no common ground to extend the conversation. All I could think of was how very clear and pink his skin was, and I could hardly ask if he invested in any particular brand of baby lotion, could I?

I used to get talking to strangers more often in the days when I queued for seats at the Old Vic or Stratford-upon-Avon. And conversations with box office staff and ushers in the stalls were all part of the process of theatre-going. It's ironic that when people say "join the conversation," they mean write something rude or angry on the internet, and that's not conversation at all. It's comment, or opinion. Conversation is a two-way give and take that has no perameters or limits and could go anywhere.

Which is why I enjoy intervals in plays. You can talk to people you know, even people you don't know, and reinforce the social occasion of theatre-going, which is its primary purpose: a shared experience of an event or performance, a dialogue between actor and audience with a right to reply at the end.

So it really does matter who you sit next to, or with, or behind. You may want to accrue moral support for your reactions, or borrow their programme for five minutes, or apologise for having coughed too much in the first act. All of these minor deeds are part of the evening's progress and will have a direct effect, perhaps only subliminally, but an effect nonetheless, on how it all pans out.

I know with whom I'm sitting at tonight's opening of Great Expectations (and, incidentally, Ralph Fiennes is truly remarkable as Magwitch in the recent Mike Newell movie, for which One Day author David Nicholls has very cleverly restructured the narrative), and at Jermyn Street on Friday for Ivor Novello's Gay's the Word (Novello's last musical; "And Gay is how we shall always remember you," wrote Noel Coward when he died).

But who will I be shoved up against in the Trafalgar Studios tomorrow night, or with whom billeted in the cosy Orange Tree on Saturday? It's a lottery, I tell you, but I hope, whoever you are, you say hello and we do a little better than Neil Kinnock and I did on Monday night.