With so little new American writing on view over here, whatever possessed Mind The Gap Theatre to honour beer as small as this three-pack of comedies by Christopher Durang? Four talented actors give it their all, but it is a measure of the plays' dramatic poverty that neither their warm-hearted performances nor the well-paced direction of Alicia Dhyana House can leaven the leaden lines they have to work with.

The first of the trio is the best, and not just because it's the shortest. The eponymous Mrs Sorken is a batty culture vulture from Connecticut, a Dame Edna grotesque who parades opinionated ignorance about matters theatrical to her captive audience, us. In Janet Prince's vivid performance, the old dear's ramblings are a tennis-elbow-foot game of thought association and an excuse for Durang to post a catalogue of theatre gags, often at the expense of his more illustrious peers (Kushner, Mamet - they must be quaking). There are chuckles to be had as Mrs Sorken's befuddled mind takes its semantic left turns, such as when a reference to ‘Seconal' triggers the word ‘secondly'…

…which brings us to For Whom the Southern Belle Tolls. This parody of Tennessee Williams's The Glass Menagerie misses the mark entirely, and as the extended centrepiece of an extremely long one-hour evening it is terminally, as well as interminably, witless. Any goodwill earned by Mrs Sorken's opening monologue fades with the realisation that Durang's highest aspiration here is to mock minority groups. Forget the moral high ground; they may be easy targets for a comedy kicking, but this writing just isn't funny.

As a dysfunctional mother-son duo, Prince and Stuart Williams chew Ji-Youn Chang's neat scenery – there is little else they could do with this material – while Melanie McHugh overacts valiantly as (you'll love this) a deaf lesbian counterpart to the source play's Gentleman Caller. Dan Frost as Tom, the brother, has to emulate the stylised 'memory play' narration of the original; but apart from that his role, like the sketch as a whole, amounts to very little.

It's a relief to reach the final furlong. Nina in the Morning, another quickie, involves all four actors again and provides Prince with a sweetly directed face-lift gag. Williams morphs from southern simpleton into French dandy, still gurning, and McHugh rushes around manically as all three of our heroine's sons. What's it about? I've forgotten already, but lubricity enters into it. At least the time slipped by.