A decade ago, Susanna Clarke's novel Jonathan Strange & Mr Norrell was one of that rare breed of books that seemed always to be glued to the hands of fellow commuters on the train.

It's a phenomenon seen, before and since, with The Da Vinci Code, Gone Girl and Fifty Shades Of Grey, although there are differences: even in paperback Clarke's book demanded reader commitment at more than 1000 pages long; it appealed to critics and won prizes (notably the Hugo and World Fantasy Awards); and, despite movie rights being sold at time of publication, rather than being deemed blockbuster material, its subsequent screen adaptation is now as a seven-part television series (BBC One, Sunday, 9pm).

Clarke's prose style, which pastiches bits of Dickens and Austen, turns this story of magic in early 19th-century England into a bit of a romp. That surely appealed to the BBC executives who green-lit the production. At a broad brushstroke, Saturday evenings are when we typically get our dose of fantasy drama (Atlantis, Merlin, Doctor Who) while Sunday is the lighter literary/costume slot (Lark Rise To Candleford, The Casual Vacancy, Poldark). Jonathan Strange & Mr Norrell would, it appears, tick both boxes.

But while Clarke's colourful secondary characters and heightened alternative-history setting suit the printed page, on the evidence of the first episode of the BBC production, a firmer directorial hand may be required in order to get the light and dark shadings of tone right.

Performances generally favoured a flash of exaggeration, from Paul Kaye's cavorting Catweazle of a street charlatan, to Marc Warren's faerie gentleman (who looks like he strolled off the screen of one of the artier Powell and Pressburger films), to Vincent Franklin's camp social climber Drawlight ("Mr NorrELLL!"). Even Strange himself (Bertie Carvel) was presented as a silly fop in these first few scenes.

But the programme could not be swallowed whole as a comedy thanks to a low-key, internalised, irritated-by-all, enigmatic turn by Eddie Marsan as "practical" magician Mr Norrell. Marsan is the reason I'll tune in for a second episode - well, him and the sly puppermaster half-smile of Enzo Cilenti as Norrell's advisor Childermass.

I've peeked ahead, and later fantasy sequences do improve on the opener's Doctor Who-standard set-piece as statues in York Minster began to move and talk. There's also the promise of the story darkening as magic becomes a strategic weapon in the Napoleonic Wars and dilemmas surround the undead life of the resurrected Lady Pole (Alice Englert). Fingers crossed, too, that the series picks up, in this timely post-election period, the book's themes of patriotism and Englishness.

There's still time for Jonathan Strange & Mr Norrell to conjure up a surprise or two.