The first half of Richard Bean’s version of Goldoni’s classic 18th century farce is the funniest 80 minutes I’ve spent in a theatre since the first time I saw Michael Frayn’s Noises Off and the last time I saw Ken Dodd. I can’t say fairer than that.

After the interval, as Kenneth Tynan said of the Broadway premiere Gypsy in 1959, the show tails off into mere brilliance. Bean’s update is set in Brighton in 1963, but it preserves the shape and dynamic of the Goldoni and, for once, the literal translation (by Francesca Manfrin) from the Italian is prominently credited in text and programme alike.

I am astounded by James Corden as the sacked skiffle player, Francis Henshall, who finds himself stretched between two sets of duties while pining for a good meal, even though all Whatsonstage.com Awards performance regulars will know how brilliant he is at bouncing off an audience as both compere and comic.

The climactic banquet served to different offstage dinner parties while Truffaldino, the harlequin, snaffles his own grub from their menus is a legendary scene in commedia dell’arte. Bean and director Nicholas Hytner take us inside the Cricketers Arms (that glorious snug pub that features in Graham Greene’s Brighton Rock) where a snooty head waiter (David Benson) and his decrepit sidekick, Alfie (played with a stricken, lugubrious terror by Tom Edden), serve up a treat of verbal hilarity and physical farce.

“A la carte?” “No, they’re going to eat in doors,” is typical of the quick-fire banter, but the great secret of Hytner’s success is the care and deliberation of the playing, so that the explosive side-effects – poor old Alfie knocked down the stairs, or flattened by an opening door, or Corden fighting his own other self and slamming himself in the face with a dustbin lid – stand out in point-making relief.

It’s a sheer pleasure, in fact, to savour the utter avoidance of some sort of chaotic mess. The plot is complicated enough as it is, with Corden signed up by Oliver Chris’s fantastic public school twit of a murderer and his own victim’s twin sister, Rachel Crabbe, who’s disguised as her own resurrected brother; in this role, Jemima Rooper is beyond brilliant as a mooching Ringo Starr lookalike with a nasty scowl gradually invaded by a melting smile.

You laugh less later, but the plot is strictly adhered to as Corden adopts a third persona of an Irish suitor and finds his way through the mayhem to a reconciliation with his own disgruntled Dolly (beautifully done by Suzie Toase) and the Cockney crime merchants (Fred Ridgeway, Trevor Laird, and Martyn Ellis as a bent lawyer speaking in tortured Latin tags) join in the fun.

For as long as Corden can stay in the production, this is certain to become one of the biggest hits in the National’s history. It’s beguilingly designed by Mark Thompson as a love letter to Brighton, and punctuated with front cloth comedy turns by the cast themselves in cahoots with a splendid skiffle band which opens the second act with a wonderful new pastiche Beatles song.