Director and producer Thom Southerland and Danielle Tarento solidify their reputation for salvaging ancient wrecks off the American coast. Having rescued Titanic equally from the icy waters of the North Atlantic and the deadly maw of a Kate Winslet movie to polish it to a high shine, they now dredge up two decrepit floaters from the shore of Long Island in Grey Gardens.

In a filthy dilapidated house of the same name in the smart summer resort of East Hampton, Jackie Kennedy’s cousin and aunt – Edie and Edith Bouvier Beale – lived a life of total squalor with 52 cats and a posse of stinking raccoons, eking out an impoverished existence of disappointment, self-delusion and scathing reciprocal recrimination, as though in some surreal Dickensian nightmare Miss Havisham and Estella made an episode of Steptoe and Son.

The main reason Doug Wright, Scott Frankel and Michael Korie fashioned a musical from these marrowless old bones is not the 1975 TV documentary which filmed them in their habitat and from which much of the dialogue is lifted verbatim, but that it attained cult status among cinéastes, gays and fans of the Whatever Happened to Baby Jane school of macabre. If anyone served rat for dinner in this hovel it would be hailed as a gourmet delicacy.

Before the decay comes an over-long first act setting the 1941 scene where young Edie is brightly betrothed to Joseph Kennedy, JFK’s navy lieutenant brother who dumped her at the engagement party but then died in action. That’s really the middle and both ends of the plot as it casts such a long shadow over the declining social status and self-respect of both women. But it doesn’t explain why they were unable to lift a dish-rag or paint a wall for more than thirty years. Old Edie dallies with a foppish pianist – super-nice work from Jeremy Legat – who may or may not also be schtupping her for cufflinks, and in a pretty dazzling debut from Rachel Anne Rayham, young Edie twirls like a ballerina in a rotting musical box as her mother serves up rendition after rendition of hideous pastiche cabaret tunes.

Even though shortened from the original off-Broadway production, Act I needs savage cuts and an audience determined to weather its tedium to get to the meat of Jenna Russell’s outstanding musical and comic turn as a 56-year-old Young Edie at the top of the second half, already the funniest thing you’ll see on stage this year. With her Marty Feldman-cowled stare prowling the audience and spitting lyrical put-downs at machine-gun speed in ‘The Revolutionary Costume For Today’ she is quite, quite dazzling and assuredly the finest musical theatre actress of her generation.

Then there’s some more humdrum amongst which Sheila Hancock shines like the Plymouth Rock lighthouse, delicately crooning her songs and defying the notion that she is actually the age Mrs Beale was at her demise: challengingly bright of eye, agile of frame and devastatingly perfect in her comic timing. The character spends some time in bed on set and it’s charming to reflect how this brings Hancock full circle to the start of her enduring celebrity as The Bed-Sit Girl in black and white television. And then when you think all hope is lost, Russell nails you again with the best number in the show, the torchy, pathos-tinged ‘Another Winter in a Summer Town’.

This isn’t a perfect storm: much of the music is forgettable, and there’s no dramatic arc, but there’s ‘something’ about it, and the publicity which surrounded this UK premiere that brought 70 critics to their feet.

Including several replacement hips.