Sydney & the Old Girl, Park Theatre review - black comedy too melodramatic

Actor Miriam Margolyes is a phenomenon. Not only has this Dickensian starred in high-profile shows both here and in Australia, a country whose citizenship she took up in 2013, but she is also Professor Sprout in the Harry Potter films. And a familiar face from television. And a voice on radio. The programme lists her 12 major awards.

Now she returns to the Park Theatre, having starred in its sellout show Madame Rubinstein a couple of years ago, in a family drama by another Park returnee, actor turned playwright Eugene O'Hare, whose bleak debut, The Weatherman, provoked controversy in its depiction of human trafficking here in August.

In her shabby East London flat, seventy-something Nell Stock (Margolyes) lives alone with her son, fiftysomething Sydney. It's a very odd situation. Although he has tried to leave home, he's never quite managed it. Both mother and son are stuck in a mutually contemptuous relationship, both aware of the emotionally devastating effect of the death, many years ago, of Bernie, Sydney's brother who had Down's Syndrome. Guilt and mutual recriminations are the emotional fuel that bind Nell and Sydney together. The family's sole visitor is Marion, an Irish home help who also volunteers for an orphan charity. Can she help mother and son reconcile their differences, or will one of them use her as a pawn in this domestic power struggle?

At first, this play begins as a comedy, not of menace so much as disparagement. Aptly enough for Guy Fawkes night, the putdowns flash and bang occasionally, but too often they are damp squibs. Neither "Old Girl" Nell nor Sydney are attractive figures: she is barely able to move from her wheelchair and is consumed with self-pity, despite the fact that she is something of a bright old bird. Sydney is the more troubled of the two: he is a paranoid virgin eaten up by hatred – of his mother, of women, of gays and of non-whites. His prejudices sting the ears and are hard to swallow.O'Hare writes with some flair, in a powerful but emotionally narrow way. He indulges Sydney's homophobia and racism with a confrontational intent that is both unpleasant and a bit alarming. The insults traded between Nell and her son – "deaf old snatch" he calls her – are initially funny in an in-yer-face way, but soon become oppressive and repetitive. As Marion gets drawn into this dysfunctional family, the plot gradually quickens, although O'Hare is unable to avoid longueurs when nothing very much happens. His viciousness reminds me of Martin McDonagh's The Beauty Queen of Leenane, but without his wit. In the end, the struggle between black comedy and sheer melodrama ends in the victory of excess rather than sense.

For fans of Margolyes, most of this might not matter. She's a great trooper, dominating the stage with her force of determination and presence. Her performance is full of expressive grimaces and wonderfully earthy verbal flights, and at times she infuses Nell with a solid Cockney humanity, her perceptions sharp and her tongue as hard as a cosh. Mark Hadfield's Sydney is more uneasy in his role, and Vivien Parry (pictured above with Hadfield) is suitably supportive. Director Phillip Breen's production, with a meticulous set by designer Max Jones and Ruth Hall, offers some fun, but O'Hare's sensibility too often fells like it's narrowly sadistic, mercilessly cruel and thoroughly unpleasant.

• Sydney & the Old Girl at the Park Theatre until 30 November
• More theatre reviews on theartsdesk

@AleksSierz