Theatre review: Untold Stories - Mama, you been on my mind

Music and Mother are preoccupations of the National's staging of Alan Bennett's memoirs

Keeping mum: Alex Jennings with Gabrielle Lloyd, poignant in Cocktail Sticks (Geraint Lewis)

Is this going to turn into Alan Bennett: The Musical? That's what you wonder, watching Untold Stories, a double bill of Bennett's dramatised memoirs with Alex Jennings as the playwright, accompanied by an on-stage string quartet.

At last week's West End press night I thought the woman seated behind me was breaking into song, but she was just crying "Awww" repeatedly, as if she wanted to chuck Jennings under the chin. Maybe this hit show's transfer from the NT has upped the risk of sentimentalisation. Personally, I like to imagine that Bennett growls whenever he's petted as a "national treasure".

Nonetheless, he is a much-loved figure, and Jennings's impersonation is a delight – almost unnervingly spot-on. Bespectacled, with short back and sides, he captures Bennett's lilting and slightly bunged-up intonation without caricaturing. He leans forward fractionally at the ankles, flaps a hand inside his tweedy jacket pocket, or sinks into an armchair with his fingers interlaced over his chest.

The first short, Hymn, is really a monologue crossed with a chamber concert, as Bennett recollects his childhood encounters with classical music and jazz. He recalls listening to the wireless, scrutinising smug orchestra members at Leeds Town Hall, and trying to play the violin as his father did, only to fall disappointingly short.

My only cavil is how Jennings, under Nadia Fall's direction, looks over-demonstratively mournful and nostalgic as the quartet launch into George Fenton's plangent score. The actor stands amid dust-sheeted furnishings, his face bathed by sunset lighting. Part of Bennett's brilliance as a writer is that he never lays it on thick, emotionally. He is too deft and wry for that. Yet Untold Stories (as the title implies) has seen him opening up slightly more, late in life, and Cocktail Sticks is an acutely touching as well as humorous portrait of his working-class parents. This second memoir is directed by Nicholas Hytner, with Jennings slipping between past and present, remembered and imagined conversations.

Jeff Rawle is quietly superb as Bennett's uxorious but antisocial father. And Gabrielle Lloyd is poignant as the playwright's nattering mam who – while her son becomes an Oxford intellectual and star, via Beyond the Fringe – naively dreams of hosting cocktail parties, is hospitalised for depression and eventually lapses into languageless senility. It's hard not to weep, although – or rather, because – Bennett remains fundamentally of the English old school that doesn't do outpourings of grief. By the way, if you're still wondering, the only point where Jennings breaks into song is in a knowingly absurd bout of jazz scatting.

In Before the Party (Almeida, London *****), Rodney Ackland's serio-satirical forgotten gem from 1949, a stuffy lawyer called Aubrey Skinner (Michael Thomas) and his Home Counties wife Blanche (primping Stella Gonet) are keen to appear impeccable, frantically sweeping improprieties under the carpet. He's angling to run as a Conservative MP and they're getting dressed up for a grandee-schmoozing bash, with their daughters in tow. However, the household's cook has just revealed she's a born-again fascist. The couple's recently widowed eldest, Laura (Katherine Parkinson), has shamelessly acquired a rakish admirer, and she's about to drag a more shocking skeleton out of the cupboard.

What's breathtaking about Matthew Dunster's production is the way it slaloms – with phenomenal agility – between a comedy of manners, a crime thriller and a tragic exposé of an alcoholic marriage. The play's ending falters, with one too many confessions, and Dunster should sling out the design team's projected cartoons, incongruously framing the action. But Parkinson is enthralling, with that husky crack in her voice venting suppressed desperation. Michelle Terry is priceless as her sourpuss sister and June Watson a trouper as Nanny, while Thomas and Gonet make hypocritical shenanigans damnably entertaining.

Finally, what about an intellectual get-together? The Salon Project (The Pit, London *) – in the season Wonder: Art and Science on the Brain – promises to costume every punter, recreating a belle époque salon where everyone can mingle with experts from neuroscience and the arts.

Being dolled up in Edwardian lace, in the Pit's dressing rooms, was a novelty. Where's the expertise for the next two hours, though? Mainly left to talk among themselves, the audience drifts around a white chamber, with fizzy wine. This is execrably lazy performance art. "Host", Stewart Laing, and "salonnière" Marcia Farquhar – neither clever nor funny – blather about clothes or announce a tableau vivant of nudes posed with iPads.

At the last minute, we're rescued by Oxford neuroscientist Professor Russell Foster and his fascinating mini-lecture on the dangers of sleep deprivation. And so to bed.

'Untold Stories' (020-7452 3000) to 15 Jun; 'Before the Party' (020-7359 4404) to 11 May; 'The Salon Project' (020-7638 8891) to 14 Apr

Critic's Choice

Proof, David Auburn's award-winning tragicomedy about maths, mourning and mental instability gets a quietly superb revival at the Menier Chocolate Factory, London (to 27 Apr). Marlowe's Doctor Faustus, updated by Colin Teevan, is at the Citizens, Glasgow (to 27 Apr), with Siobhan Redmond as Mephistopheles.