Like their brilliant show about the privatisation of the railways ten years ago, Out of Joint's latest is about something we all care passionately about – one way or the other – the National Health Service.

While politicians of all parties commit casuistry on a daily basis when it comes to reports, discussions and parliamentary bills on how to improve, save or stealthily undermine the greatest beneficial institution of our post-war era, those of us who have enjoyed those benefits – and they include this terrific show's director, Max Stafford-Clark, who suffered and survived a debilitating stroke in 2006 – will be cheering on his committed cast and the surrounding campaigns.

Re-animating some fairly antiquated agitprop methodology – rudimentary sketches, disruptive plants in the audience, the political ghosts of Churchill and Nye Bevan, the NHS personified as a last-gasp crone on a hospital bed – Stella Feehily's angry and agile script still manages to create a coherent drama around the story of one elderly patient, Stephanie Cole's feisty old Iris, laid low with a suspected stroke that turns out to be a rare case of transient amnesia.

We sidle into Iris, as it were, through Brian Protheroe as her son, a widowed former teacher, Nicholas, who is testing for prostate cancer while discovering at first hand the strains on the system (unhelpful receptionist, a consultant who airily says that, if you want an earlier appointment, make it a private one) and doubling briefly as a gruesomely hapless David Cameron trying to make sense (and political capital) out of New Labour policy expressed in a labyrinthine report.

Iris's daughter, Mariel (Jane Wymark), a privatisation apologist, is married to a ghastly American osteopath (William Hope), visiting Britain on a conference, and their resultant ideological stand-off over Iris's bed climaxes in the funniest hospital ward scene since Peter Nichols's The National Health over forty years ago.

While the siblings bicker - and Wymark's real-life brother, Tristram Wymark, gibbers away in a wheelchair as a stroke victim and at one point grabs his own sister's right breast – a corpse lies unattended behind screens, a hospital porter loses a patient, there's blood on the ceiling, and an overworked nurse (Natalie Klamar) throws a complete wobbly.

There is nothing here like the television bromide of Casualty or Doctors. This is theatrical distillation, using light weaponry of satire and cartoonery – an update on the state of play in the nation's hospitals is delivered as a simpering weather forecast – to make a drama out of a genuine crisis.

Nurses have had their pensions, and now their numbers, cut. Accident and Emergency wards are being "rationalised" (ie, closed down). Private finance builds the infrastructures that are then sold on to public services, incurring huge debts in those services which leads, or will lead, to a political validation of privatisation.

Hywel Morgan's Nye Bevan is passionately resurrected to lay down the principles of 1948, while Frances Ashman contributes a quartet of brilliantly contrasted operators in the system and Stephanie Cole, effortlessly authoritative and delightfully foul-mouthed, suggests as Iris that the way forward lies in a heroic collaboration between a conscientious public and the medical profession on the ground.