Acadia Repertory Theatre’s new production of “Relatively Speaking,” Alan Ayckbourn’s mistaken-identity comedy now playing through Aug. 10 at the Masonic Hall in Somesville, is a lesson in first impressions. Usually you can trust them. Not this time.

The first scene is a slow-burning and rigid introduction to Greg and Ginny, young English lovers whose relationship, secret affairs and miscommunications are the central theme of Ayckbourn’s clippy script. Except the clip is missing. David Blais, as Greg, is perfectly animated, but Kimberly J. Forbes, as his paramour, takes the long road to reaching her character’s destination. She eventually gets there, but it takes the rallying expertise of the rest of the cast to nudge her along toward the particular flair of English absurdity.

The action really gets going in the second scene – or, more accurately, in the set change between the first and second scene, when Keystone Kops (though Brit style) stage hands comically transform Greg and Ginny’s London flat into a garden patio in the Home Counties. Background music by The Swingle Singers, whose jazz a cappella harmonies are hilarious in their own right, steers the mood upward. By the time the lights come up on that setting and we meet an older couple, Philip and Sheila, whose true identity it would be so wrong to reveal here, the audience is ready to rock.

Played by the real-life husband-and-wife team Fred and Liz Robbins, Philip and Sheila take up that task. They personify the undisturbed complacency of the bourgeoisie, a stock in trade for Ayckbourn whose work has been regularly staged by Acadia Rep. Sipping tea in the Sunday morning sunshine, they marvel at their garden as they chide one another politely for allowing their marriage to grow stale.

They have no idea what is in store for them when first Greg and then Ginny shows up on their doorstep.

Director Ken Stack, the local master of madcap comedy and spunky sets, clearly knew that success would follow the Robbinses in these roles. Some might find Fred’s constant gesticulatory mumbles distracting or too cartoonish. But, again, first impressions will not linger long. Fred is very funny and his comic timing is superb. As Sheila, Liz gives a flawless and intelligent performance of a perplexed but game partner.

Together, they add the exact splash of refreshment that this production requires after such a draggy start. They bring the clip, and the rest is standard Ayckbourn frippery. By the end, all four cast members can rightly claim their applause – but it would be wrong not to acknowledge the considerable amount of brightness that Blais adds throughout the show.

It is nearly obligatory, if somewhat annoying, to mention that Ayckbourn has been persistently called the Neil Simon of England. His name also appears rightfully alongside heavyweights Harold Pinter and Tom Stoppard. But it’s best to see Ayckbourn – who has written more than 40 plays – as his own voice, trimmed of excess yet dedicated to jolliness.

Acadia Repertory Theatre will present “Relatively Speaking” through Aug. 10 at the Masonic Hall in Somesville. For tickets, call 244-7260.