Antony Jay and Jonathan Lynn have taken the elements of their superlative television series and distorted them in this two-hour stage adaptation, which now returns to the West End with a new cast but the same plodding script.

The setting has been dragged pretty successfully into the 21st century, with Jim Hacker (Richard McCabe) now the leader of shaky coalition government in the midst of a global economic crisis and Sir Humphrey Appleby (Simon Williams) applying his powers of Machiavellian manipulation to the Prime Minister’s Blackberry. A £10 trillion loan from fictional south-Asian country Kumranistan is on the table, and during one fraught night in Chequers the Prime Minister must fend off both Appleby’s plans to coerce the country into the Euro and the Kumranistan minister’s perverse expectations of UK hospitality.

The elements are all in place for brilliant farce and biting satire, but instead we descend into a brash, hysterical and rather grimy pantomime.

The Kumranistan minister’s request for the sexual favours of an underage girl falls on the auditorium with a sickening crunch. Was there an element of truthfulness or contemporary understanding in the script then such a plot thread might be seen as an envelope-pushing engagement with a difficult subject matter, but when played for cheap and hollow laughs, it’s a tasteless misstep.

It's at this moment that the beloved characters Jay and Lynn created leave the stage for good; Hacker is appealing because, despite his egocentricity and flexible morality, he has the interests of common people somewhere in his heart. Here the living character has been scooped out and his shell filled with a venomous attack on the figure of the politician. Hacker endorsing the procuring of a sex-trafficked underage girl to be raped in Chequers, and then gleefully planning to leave her to rot in a detention centre robs the character of any likeability. Meanwhile, Sir Humphrey seems to vanish from proceedings altogether, his playfully demonic presence hardly required in a room of ranting, wisecracking monsters.

Elsewhere, the script is a hodgepodge of contemporary hot-topics. Global warming, the size and cost of the BBC, Britain’s position in the EU, the invasion of Iraq - all are visited without the intelligence and insight the TV programme so ably displayed 30 years ago. The best jokes are cribbed from those earlier scripts, while new ones rely on tired platitudes (‘murder and prayer’ is the American way) and cringe-worthy concessions to modernity (eg Twitter exists).

The show's saving graces come in the form of Williams’ strong turn as Sir Humphrey, giving the character the toothy veneer of a game-show host which works quite brilliantly and escapes the considerable shadow of Sir Nigel Hawthorne, and a brilliant design by Simon Higlett. The detail lavished on the set far outstrips the few hastily decorated offices of the BBC original. In other respects, however, this is a disappointing coda to TV’s smartest half-hour.

- Stewart Pringle