When Peter Nichols wrote A Day in the Death of Joe Egg in 1967, I was doing Wednesday afternoon ‘voluntary service’ to get out of school games, at the Yorkshire Association for the Disabled – a massive residential facility in the middle of Harrogate. It also helped that my mother worked there in the accounts office, and would give me a lift home afterwards.

What struck me, though, apart from the opportunity to engage with friendly residents like diminutive hump-backed Annie Donald who I am sure had a crush on me, or the wheelchair bound Billy Glaves who’d been injured in a motorcycle accident – and, incidentally, eventually married Annie – was that everyone, from the Head Nurse to the most junior porter referred to all the inmates as ‘The Spazzies’.

I supposed we called each other ‘spastic’ at school, in ways that some boys later substituted ‘gay’, and the charity Scope which focuses on cerebral palsy only changed its name from ‘The Spastics Society’ in 1994.

But is still caused a gasp in Simon Evans’ excellently paced and detailed production at Trafalgar Studios.

Jo, the disabled child who’s the focus but not the principal character is daughter of sink school teacher Bri and his affectionate wife. Storme Toolis, as the first actually disabled actor to take the role in a major production, varies stillness and tremor, silence and articulation with panache.

What’s at stake are the parents’ different coping mechanisms: Claire Skinner’s Sheila takes pride in her nurturing homemaking and seeks refuge in amateur dramatics, Toby Stephens’ outstandingly sardonic Bri staves off despair with dark humour and harmless fantasies mostly about sex with his wife.

All good domestic banter needs a convincing audience of innocent bystanders – a pattern repeated in Abigail’s Party a decade later, and Joe Egg is well served by the second act intervention of two friends from Sheila’s Am Dram group, effortlessly well done by Clarence Smith as the bombastic do-gooder we’d all cross the pub to avoid and Lucy Eaton as the polite audience’s suppressed inner voice allowed to express revulsion at coming so close to disability.

Her treatise on euthanasia must have been hard for Nichols to write, but is hilarious when delivered so well. In her rejection of anything ‘not physically attractive’ she’s a prototype for the WAG generation.

Although Sheila claims to have picked the items up at charity sales, the set is perhaps a little too upper middle for the period and Bri’s teacher’s salary, so it’s a surprised and delight to see Patricia Hodge bring him down a peg or two in her terrific cameo as his soundly Bristolian working class mother.

Ensemble acting of this quality is rare enough at any time, but it’s the best cast you’ll currently see in a comedy in the West End, and may make you wonder what all the noise and capering is about in higher profile shows.

Don’t miss it. Makes you laugh, makes you think. Makes you realise Stephens is one of our finest.