Those of us who hoped David Hare’s latest play would live up to titillating advance reports and launch a direct attack upon the Blair administration’s loose morality, its dogged pursuit of financial donors to the party and that prime minister’s love of big money, were disappointed last night. Hare never really faces up to the eternal problem of deciding whether political parties should be financed by public money or should raise their own funds from business or trade unions — with all the attendant threat of corruption.

Instead Gethsemane mixes a heady, soap-operatic cocktail of sex, drugs and scandal, symptoms of materialistic, immoral times. Once again Hare puts our body politic through a head-to-toe scan and finds it rotten to the core. Anyone, though, seeking to draw comparisons between Gethsemane’s labyrinthine plot and the world of Tony Blair is supposed to be warned off by Hare’s programme note, identifying his play as “pure fiction... drawing on public events”. Well, I wondered about this all the way through the labours of Gethsemane, as big business, the media, and supposedly fictitious politicians were caught in a single, unlovely coil. Impure, perhaps, would be a more accurate adjective for Hare’s lurid scenario. A scandal involving Suzette, the angry daughter of a fictitious home secretary, Meredith Guest, is damped down with a bribe paid out by Otto Fallon, a hairdresser turned millionaire and money-raiser for the Labour party. Otto, whom Stanley Townsend plays with stubble beard, long hair in a small plait and a manner of unctuous charm, broods over a political scene beset by corruption.

Jessica Raine’s Suzette, superb in her adolescent scorn, precipitates Gethsemane’s psychologically unpersuasive action. The teenager falls from druggy disgrace to potential disaster, when she gladly becomes the sole attraction in a small orgy involving four grown men, one of whom is a newspaper columnist whose proprietor is awaiting trial on fraud charges. We are to understand Suzette, and the mode is all too clichéd, as a disturbed adolescent helped solely by Nicola Walker’s teacher turned busker — the play’s fount of morality. Jessica’s father faces business charges abroad while her mother faces up to Anthony Calf’s suave, devious, drum-playing prime minister and struggles to save her Cabinet post.

In this powerfully acted scene, fascinating with its fraught nuances and veiled threats, Hare conveys a sense of political conflict and a subtlety otherwise missing. And Tamsin Greig endows Meredith with an imperious charisma and well-dressed assurance as she puts career before principle.

Written in 17 scenes, whose locations are vividly conveyed by video projections, Gethsemane loses its sense of purpose in the rambling diffuseness of its hectic plot. Hare is beset once again by an understandable fury that the high hopes of Labour have been dashed on the rocks of warfare, with socialism diluted to watery insignificance.

Howard Davies’s suitably cool production cannot disguise the fact that the melodramatics of the action are not well suited to a play intent upon lamenting the decline and fall of Labour.