Dion Boucicault is remembered today for inaugurating modern Irish drama with The Colleen Bawn, his huge success of 1860. London Assurance belongs to an earlier, very different phase of his work. It was written in 1841, when Boucicault was a penniless, twenty-one-year-old adventurer newly arrived in England and determined to impose himself on the London stage. While The Colleen Bawn looks forward to Synge and O’Casey, London Assurance commandeers the comic conventions of Sheridan and Goldsmith, pushing them to extravagant lengths surreally within earshot of The Importance of Being Earnest. Opportunities to see this odd, exuberant play are rare, so it is good to find Jacob Murray directing a full-blooded, fast-paced production, which communicates the play’s youthful impudence (the “assurance” of the title) and leads its cast of grotesques a lively dance.

London Assurance gives us the outsider’s view of English society. Almost every character is given plentiful soliloquies and asides; we see the action from a multitude of egocentric and cranky viewpoints. Both acts open with scathing dialogue among the servants: the gentry never have a chance to be taken at their own valuation, and Murray Melvin gets the play off to a fine start with his vignette of the footman Cool, splendidly emaciated and melancholy, surveying the antics of his employers with apocalyptic gloom.

Gerald Harper - with plucked eyebrows and rouge, curled black wig, brocade dressing gown, and lorgnette - is an imposing and ludicrous presence as Sir Harcourt Courtly, the fossilized Regency beau convinced that he can pay his debts by marrying eighteen-year-old Grace Harkaway. A magnetic presence on stage, Harper enhances Sir Harcourt’s orotund pomposity and mangling of fashionable French words with a gift for physical comedy. His difficulties in “decanting himself” from a top hat without dislodging his wig are memorable. He finds an able sparring partner in Race Davies as the cigar-smoking, fox-hunting Lady Gay Spanker, a formidable auburn-haired Amazon in fox-red silks and velvets. Intimidating and then seducing Sir Harcourt, summoning her tiny, stammering husband Adolphus (“Dolly”, played by Peter Lindford) with a dog-whistle, she communicates the sexual charge which the play needs but which the nominal heroine, Rae Hendry’s demure and absurd Grace Harkaway, necessarily lacks.

Hendry gives us a pert Grace, full of unfounded self-confidence. Aware that “marriage is conducted nowadays in a most mercantile manner”, she is perfectly happy to evade the entail on her father’s estate by marrying Sir Harcourt without first meeting him. Hendry plays her with a nicely contrived cynicism, and copes bravely with her parodic soliloquies ludicrous rhetoric about brooks, flowers, and “the thrilling choir of the woodland niinstrels” - though at moments she overdoes the gentility, her enunciation becoming so lisping that it is hard to make out what she is saying.

Charles Aitken as the young hero Charles Courtly has some of the play’s best speeches. Confronted with Grace, he inevitably staggers into a verbal and logical morass while trying to match her genteel rhetoric (“When a man throws his feet at your head - no, I mean when he throws his head at your feet - no, I mean when he throws his heart at your feet ...”) or in pointing out the consequences of his father’s proposed marriage (“Consider my position! A few days - and I would have been your mother.

No, you would have been my father - no, you would have been my mother!”). He, too, has his opportunities for mime. The deliriously implausible plot demands that Charles keep his father, Sir Harcourt, at bay by pretending to be a bookish recluse, while meeting Sir Harcourt in public as his son’s supposed double, the urbane Augustus Hamilton. Aitken’s physical transformations from the robust Hamilton to the hollow-cheeked, knock-kneed, round-shouldered Charles are quite disturbingly convincing.

At the enigmatic heart of the play is the raffish Dazzle, played by Andrew Langtree. As Dazzle cons and improvises his way from Belgravia to Gloucestershire, it is tempting to see him as Boucicault’s wry self-portrait, the more so when he acts incidentally as deus ex machina, resolving other characters’ problems without finding a niche for himself. Langtree gives him immense panache, but adds a tinge of desperation. His final confession that he has “not the remotest idea” who he is, beyond being a liver on credit, a backer of winners and “an epidemic on the trade of tailor”, adds a concluding touch of metaphysical strangeness. There is something here for everyone, from children to theatrical historians, and the Royal Exchange’s astuteness in choosing London Assurance as their Christmas production would certainly have won the applause of Boucicault, who knew a good bet, when he saw it.