Future Conditional (Old Vic Theatre)

British education, or rather the damage done to it by successive parliamentarians, makes Tamsin Oglesby angry. Really angry. So fired up is the author of Really Old, Like Forty Five that she's poured all her outrage into this big, fulminating play, and it's a mess. Perhaps cooler heads were needed.

Yet Matthew Warchus has selected Future Conditional to open his account as artistic director of the Old Vic, and a stranger choice would be hard to imagine. If it's state-of-the-nation drama he was after he could surely have done better than Oglesby's epic in which, with a scattergun in one hand and a battering ram in the other, she blasts the system but posits no answers apart from one breathtakingly naïve idea about university admissions.

Fundamentally she is saying that Michael Gove and his ilk have diminished us all: the parents who flounder in an unfair admissions process, the teachers who struggle to maintain discipline in a child-centred world, the quangos (here a fictional 'Education Equalities Commission') whose members are hamstrung by their own educational background.

But there's too much going on as the action jumps around between these worlds. And the incidental comedy, such as it is, isn't exactly organic. "There's not a level playing field because the playing fields have been sold off" sounds like one from the notebook.

Warchus harbours no doubts though, and he directs with his customary verve, knitting the material together with rock guitar interludes that brighten the pace while expertly marshalling a 23-strong cast within Rob Howell's in-the-round designs.

Rob Brydon, playing it straight, has touching solo moments, not least when he attempts under sufferance to draft an apology to the appalling mother of a difficult child. Other than that he's limited to occasional appearances as a good teacher faced with difficult pupils. Or, weirdly, not faced, as none are visible to us apart from the brightest of them, Alia (Nikki Patel). She is the only character who's allowed to move between the sub-casts and her guileless wisdom shows up the inadequacies of her elders.

Six mums whose children, also invisible, are making the transition from primary to secondary education have the lion's share of the action — unsurprisingly, since this is an area where Oglesby has been badly bruised in real life. The actresses work hard but can do little with the lazy stereotypes they are obliged to embody, and their scenes are an exercise in cliché. "The eclecticism of the parents", as one of them sighs in a telling meta moment.

The Commission's meetings are a class-divide sub-plot that's treated as an excuse for broad character comedy, with unintegrated joke-telling, sizeist insults and cake-chucking among its subtler pleasures. Only the play's framing scenes, which look perceptively (and, from my own experience, pretty accurately) at the insular haphazardness of the Oxbridge admission process, achieve much distinction. For the rest, Future Conditional falls a long way past imperfect.

Future Conditional runs at the Old Vic until 3 October.