Who needs a script? How ad-libbed shows are taking over the schedules

In comedy, it seems the deceptively difficult art of ad-libbing is everywhere, from feature-length "mockumentaries" such as In the Loop, Brüno and Borat, to the award-winning television series The Thick of It and Curb Your Enthusiasm.

Increasingly, the best comedies, such as those lauded in the British Comedy Awards this weekend, ignore the show-business adage about sticking to the script by throwing in a hefty dose of spontaneity.

Outnumbered, the BBC's contemporary "comedy of the Noughties", based around an unconventional suburban family, won a trio of awards at the ceremony last night, including best sitcom and best overall comedy.

The wonderfully caustic The Thick of It, which stars the foul-mouthed Peter Capaldi as the Whitehall spin-doctor Malcolm Tucker, works, he says, because they take the script and "put it in their own language. Sometimes that can be funny, sometimes it's not". In the Loop, the show's silver-screen spin-off, was named best comedy film at the awards last night, while the veteran ad-libber Sir Terry Wogan, who retired from his long-running Radio 2 breakfast show this month, was given a life-time achievement award.

The comedian Catherine Tate is said to have ad-libbed some of the best-known lines in her eponymous show, including sketches with the foul-mouthed grandmother Joannie "Nan" Taylor. Tate once said that when she first started out, she had "nothing concrete and certainly nothing written down". "Few things focus the mind like fear," she added.

In the US, the Emmy award-winning Curb Your Enthusiasm was, according to its recurring character Ted Danson, ad-libbed thrice over to enable the writers to form an impromptu script, so that Larry and the team could "go back to being actors".

The New Zealand musical comedy duo Jemaine Clement and Bret McKenzie of Flight of the Conchords say that many of their show's funniest lines are improvised, too, a skill they credit mainly to Rhys Darby, who plays the band's hapless manager, Murray. He's so good at it that he "ad-libs his ad-libs", coming out with lines such as "I'm so livid with you turkeys. You're like a couple of cool-looking idiots".

That Outnumbered's trio of child comedians manages to produce exceptional performances is a testament to their ability. The youngest, Ramona Marquez, eight, who was named best female newcomer last night, has, according to its director, Andy Hamilton, "the face of an angel and the mind of a barrister". He knew only too well the difficulties of getting children to act after casting his own daughter, Isobel, then seven, in Bedtime, his 2001 comedy series. What he learnt stayed with him – and in Outnumbered, neither Ramona, nor her fellow child star Daniel Roche, is permitted to see the script. Instead, they're briefed with a rough outline of what they're supposed to do before each scene is shot – and the rest, as they say, is carnage.

Guy Jenkin, the show's co-writer, who also worked on the newsroom sitcom Drop the Dead Donkey, gave an example: "We wanted Ramona to say, 'You smell like you've been to the pub. She actually said, 'You smell of pub'. It's more like a child, and funnier."

But ad-libbing can rebound on performers, as Jonathan Ross found. After last year's "Sachsgate", Wossy was banned from hosting the prestigious awards. Last night he was back, and in favour again, it seems: ad-libs and all.

Every One A Winner

Best comedy entertainment personality: Harry Hill, Harry Hill's TV Burp (Avalon for ITV1)

Best comedy entertainment programme: Harry Hill's TV Burp

Best TV comedy actor: Simon Bird, The Inbetweeners (Bwark for E4)

Best TV comedy actress: Katherine Parkinson, The IT Crowd (Talkback Thames for Channel 4)

Best new British TV comedy: Psychoville (BBC Productions for BBC2)

Best TV comedy drama: Pulling – special (Silver River for BBC3)

Best live stand-up performer: Michael McIntyre Live at the Apollo

Best male comedy newcomer: Charlie Brooker, You Have Been Watching (Zeppotron for E4)

Best female comedy newcomer: Ramona Marquez, Outnumbered: series 2 (Hat Trick for BBC1)

Best comedy panel show: Have I Got News for You (Hat Trick)

Best sitcom: Outnumbered

Best sketch show: Harry & Paul: series 2 (Tiger Aspect for BBC1).

Best comedy film: In the Loop (Optimum Releasing)