Fay Weldon is anything but predictable. Long claimed by feminists as one of their own, albeit one who refused to stick to the script, she has become, in recent years, an outspoken advocate of men's rights. After decades of urging women to be bad, she concluded in 2006's What Makes Women Happy that the answer was being good  and chocolate. Several years ago, at the age of 69, and after a lifetime of atheism, she was baptised into the Anglican church.

Such apparent volte-faces should come as no surprise. Since she published The Fat Woman's Joke in 1967, Weldon has defied categorisation. Experimental in form, and vernacular in style, her work is distinguished not only by her virtuosity as a writer but by her fearlessness, her refusal to accept orthodoxies. From plastic surgery and cloning to corrupt politics and the spread of militarism, her novels explore subjects that are both topical and controversial. Her dissection of ordinary lives is always sharp-eyed and frequently shocking. In Weldon's world, women are not docile, domestic creatures but angry and implacable. They binge-eat, hate their children, burn down their houses, and exact revenge against their faithless husbands; often, they are to blame for their own predicaments. They are also brave, feisty and extremely funny.

The prospect of Weldon's vigorous iconoclasm being brought to bear on the historical novel was therefore thrilling. It seemed particularly characteristic that she would choose to set her story in 1899, an era whose charms have been so relentlessly milked. Weldon herself wrote the pilot episode for the original series of Upstairs, Downstairs; since then the period has been worked over exhaustively by romantic novelists and glossy Sunday night dramas such as Downton Abbey. Awash with cliché and stock characters, turn-of-the-century London seemed ripe territory for Weldon's subversive pen.

The novel opens with the clamorous dawn arrival at 17 Belgrave Square of Mr Baum, a young man deemed by Grace, the lady's maid who spies him from the window, to be "too young, too excitable and too foreign-looking to be worthy of much exertion". Though the household resolutely ignores Mr Baum's summons, so that the master of the house himself is obliged to open the door, it transpires that he has brought news that is to prove potentially catastrophic to the Earl of Dilberne and his family, and which considerably intensifies the countess's desire to marry off their two adult children profitably and without delay.

With nearly one hundred pages devoted to this inauspicious day, the stage is set for a comedy of manners. Weldon has kept her focus narrow, so that although contemporary politics occasionally impinge, it remains almost exclusively domestic. The plot might flatteringly be called flimsy, but this would have mattered less if Weldon had not borrowed her characters directly from the BBC casting cupboard. They are all here, from the doughty cook and the frustrated housemaid to the stodgy but reasonable-minded earl and his two children, the dilettante, spendthrift heir and his difficult suffragette sister who refuses to marry; most are sketchily drawn, as though they are awaiting a charismatic actor to breathe some life into them. Stereotypes are rife. The English upper classes are uptight and hypocritical; new-money Americans are vulgar and brash and do not know the proper way to address a servant. The servants are grumbly but good-hearted. They even have names like Grace and Smithers. If there is irony intended here, it is not sufficiently in evidence. Extended paragraphs of reported speech, not to mention exhaustive descriptions of the characters' outfits, add to the impression of a book written primarily as an outline for a television series.

The novel has some funny moments, such as the scene when the earl's son Arthur encounters his old Eton fag in flagrante with the prostitute he understood to be his exclusive property. The relationship between Arthur and the American heiress his family would have him marry is fresh and endearing enough to have one rooting for a happy ending. But the treats are too few and far between. Habits of the House is lacklustre, a pastiche without a purpose, lacking both the intellectual heft of Weldon's previous novels and their sly savagery. Endless discussions of dinner menus and Liberty patterns and the complexities of social etiquette might provide a convincing exposition of the dullness of being an Edwardian aristocrat but they do little to enliven the narrative.

Weldon's prose has an easy grace that ensures that the pages slip by without undue difficulty, but they don't stick. One is left craving the verve and originality of her earlier novels and wondering just what it was about this story that made her want to write it in the first place.

 Clare Clark's Beautiful Lies is published by Harvill Secker.