Of course, the seat in question is one you sit on, not sit with, and Gemma has sportingly taken part in the Almeida seat-naming programme ("minimum suggested donation £1,000"), having recently helped to fill a good few of them as Hilda Wangel in The Master Builder opposite Stephen Dillane.
I arrived early at the Almeida for the opening last night -- you can't afford to take any chances with the North London line at the moment -- and enjoyed sharing a snack and a drink with actress Karen Lewis, wife of artistic director Michael Attenborough.
Karen was filling me in on her recent New York appearance in an early John Osborne play, and the burgeoning theatrical careers of the new Attenborough generation.
She and Mike have two sons: Tom is a director, and is reviving, next week, Neil LaBute's coruscating The Shape of Things at a new venue, the Gallery Soho, in the Charing Cross Road (this was the play that Harold Pinter stormed out of before it even began, on account of the loud punk rock music blaring out in the Almeida's British premiere, starring Rachel Weisz, at the abandoned bus station in King's Cross); and young William is acting his head off as a Cambridge undergraduate. His schoolboy Hamlet was scarily good, declares proud Mum.
Anyway, as Karen and I pushed through to the main body of the First Night throng, we suddenly ran slap bang into Gemma, and just as Karen turned to introduced me...I ducked away and melded with the crowd.
Why? Because the last time I saw Gemma, she was stark naked, manacled to a bed and thrashing her limbs in a vain attempt to escape her kidnappers. I was suddenly, and unaccountably, shocked to see her with her clothes on.
Yes, I've just caught up with The Disappearance of Alice Creed -- and a damned fine movie it is, too -- and I felt I was already on sufficiently intimate terms with Ms Arterton to excuse me the effort of trite conversation.
I was on much safer ground catching up with director and Almeida board member Giles Havergal and his globe-trotting projects in San Francisco, New York and Australia (where he is just about to take his Opera North production of The Merry Widow).
Becky Shaw itself proved a pleasant, unexpected suprise, especially as it originated at the Humana Festival of New American Plays in Louisville, Kentucky, where I don't think they've had a hit play since The Gin Game.
There was a time when London critics were invited, all expenses paid, to attend the festival; they even gave you an air ticket you could break for a New York stopover. But the plays were so bad, it became embarrassing to accept the hospitality in exchange for the damning reviews that inevitably followed.
But Becky Shaw changes all that. And if there's a sniff of another invite to a future festival in Louisville, home of the horses, rare roast beef and best bourbon in the world, I'll look at it not quite so disconsolately again.
Odd that Becky Shaw is mispronounced in the play as "Becky Sharp", the Thackeray heroine of Vanity Fair whom she vaguely resembles. It was a night of soundalikes: David Wilson Barnes as the wonderfully detestable Max looks and even sounds uncannily like Kevin Spacey.
And one of the characters is called "Andrew Porter" but looks and sounds absolutely nothing like his namesake, the distinsguished and venerable music critic who is outed in Michael Codron's recent autobiography (co-written with Alan Strachan) as one of the impresario's closest friends and lovers during his Oxford days.
Back to Gemma: I can still claim her as one of my Essex girls as she hails from my neck of the woods. Romford, to be precise, home town, too, of Liz Robertson and Michelle Dockery.
Next time I bump into her, I'll pluck up the courage to say hello, even if she is fully dressed.