With 2005's The 40-Year-Old Virgin - in my book, one of the three best American comedies since the turn of the century (Stuck on You and Borat being the other two, in case you're wondering) - the writer-director Judd Apatow announced himself as a truly adult filmmaker: one terrifically funny and filthy of mind but pure of heart. His follow-up Knocked Up plots the circumstances leading up to - and the consequences of - one of the more unlikely hook-ups in recent screen history: that between chubby slacker Ben Stone (Seth Rogen) and eligible, Britney-esque blonde Alison (Katherine Heigl), who retire to the latter's place after a drunken encounter in an L.A. nightspot.
It's no surprise to learn the pair part soon after, as a result of irreconciliable life differences: she's an ambitious producer-turned-director for the E! network, while he's a dyed-in-the-wool stoner who can't even get a celebrity porn website up-and-running; his idea of an appealing proposition is "I'll show you Meg Ryan's bush". (I'm guessing Apatow's research must have been an eye-opener.) One night, Ben gets a call out of the blue: it's Alison, and she's pregnant, a situation Ben doesn't take very well - a disbelieving "fuck off" is the precise term deployed - but comes to live with over the subsequent nine months.
From one shot of Rogen's flabby, spotty, hairy buttocks as observed on the morning after Ben and Alison's first tryst, it's possible to identify Knocked Up as a film with precious few illusions or preconceptions about modern love. The dramatis personae here include men who won't (or find it hard to) grow up; women who are held back from personal fulfilment by a unrelenting insecurity around other women; and a married couple (Leslie Mann and Paul Rudd) whose underlying resentment of Ben and Alison's first-flush happiness very nearly results in divorce.
From his first two films, it's become apparent that Apatow is at heart a traditionalist, interested in the ways men and women interact these days, but he's one forever careful to overwrite the conventional sex comedy's standard-issue scuzziness and cynicism with a pervasive and persuasive sweetness. His gift lies in finding new ways to tell the same old stories: tossing in dirty jokes, plentiful pop-cultural references (Rogen and Rudd's "you know how I know you're gay?" schtick from Virgin here morphs into a homoerotic reclamation of dialogue from Back to the Future: "I'll strap you into my DeLorean and get you up to 88") and moments of gross-out comedy (a prosthetic vagina features as the baby starts crowning).
Knocked Up's finale reverts to fairly conventional cooing at a newborn in swaddling clothes, but up until that point, it makes for a most enjoyable romantic comedy of unpredictable events, both at plot level (in the unexpected declaration of pregnancy that brings the two leads together) and on a scene-by-scene basis (in the spontaneity Apatow fosters in his performers). Rogen remains entirely convincing as both a fuzzy sleazeball jerk - the type of guy who accuses others of watching films without nudity as though it were the worst crime a red-blooded male could commit - and as the most redeemable figure among a set of bearded, grungy no-hopers who'd rather dash off to see Spider-Man 3 than do any work.
Heigl is game enough to play a young woman who is, at various points, at least ten years more mature than any of the men in her life, hormonally unreasonable, and all too willing to submit to her man's less perverse desires, helpfully enumerating the nude scenes in Carrie, which is one way for lovers to bond; her shake of the head when presented with faced with Neve Campbell and Denise Richards' swimming-pool liaison in Wild Things - a scene that has always played better with men than with women - is possibly the truest moment in the picture. Around them, Apatow has gathered a supporting cast whose asides and adlibs take the film, and its constituent relationships, off in entirely different directions.
It's here Knocked Up starts to suffer, because after The 40-Year-Old Virgin (two hours plus), Apatow appears a director unusually fond of his own deleted scenes. At 129 minutes, Knocked Up is a longer film than its predecessor, and a mushier film, when it finally gets round to it: Virgin climaxed with that wild and wonderfully wayward Hair pastiche, but this latest starts showing you baby photos, like an insistent parent. Too many sequences require Rogen to say something tactless and blokeish, and for Heigl to roll her eyes or storm out before taking her unlikely suitor back. (Wouldn't it have been more interesting if Alison had had a rival for her affections?)
Still, if there's a lot of Knocked Up, then a lot of it is a lot of fun, and it's hard to know what one would have left on the editing room floor. The inappropriately joshing gynaecologist? Rudd and Rogen's boys-night-out in Vegas, at the end of which the former ends up glassy-eyed in his appreciation of hotel-room chairs, while the latter is confronted by the sight of Steve Martin in Cheaper by the Dozen? A montage of sex scenes illustrating male fears about the pregnant female form, each one scored to a different Terence Trent d'Arby song? Even if there are sometimes problems with the delivery, Knocked Up is pregnant with wonderful comic ideas.
Knocked Up screens on ITV1 tonight at 10.35pm. A semi-sequel, This is 40, opens in cinemas on Friday.