Graham Linehan, one of his writers, explains. "If you get kids repeating your lines in the school-room the next day, then you've got success. I remember everyone doing Neil and Rik from The Young Ones when I was school. It's important to anchor jokes in people's minds. Catchphrases aren't artifice. People do have them - they just don't realise they do till someone points it out."
Arthur Mathews, Linehan's writing partner, concurs. "I like the relentless nature of catchphrases. You're just dying for the character to get to it. They offer familiarity. They're cosy and reassuring. It's like when you go and see a band, you always want to see them play the greatest hits rather than new stuff."
Despite that, the new series of Harry Enfield and Chums features plenty of new material which is sure to spawn greatest hits before the end of morning break. Bizarrely, the series is released on video next week before being broadcast on BBC1 in the New Year.
In one clever new sketch, Enfield and sidekick Kathy Burke climb into babygrows to play The Toddlers; the "catchphrase" here is a continually repeated schtick in which he gets her into trouble with their mother.
Later, Enfield dons a ludicrous Hardy Kruger-style blond wig to play a breast-beating tourist called "Jurgen the German", who goes around accosting unsuspecting Brits and telling them: "I feel I must apologise for the conduct of my nation in the war." "It's hideously racist," Enfield concedes with a laugh. "But we like taking the piss out of the Germans because we're jealous of them. Even mini-cabs out there are Mercedes."
For all that, Enfield claims to like his characters. "I've got sympathy for them all," he contends. "I'm never going, `look at them, aren't they wankers?' It's affectionate. And people like having the piss taken out of them. You see people on the terraces at Liverpool in Scouser wigs and moustaches. Most of my characters are silly little boys. It's human. Everyone is badly behaved."
This is a man with a seemingly endless capacity to delve around in the dressing-up box and come up with something new. His mine of fresh - and absurd - characters shows no sign of exhaustion yet. The character's the thing for Enfield. "With other character comedians, you know what they're like in real life," Linehan observes. "With Harry, you don't. Harry is his characters. He's more interested in character than a good sketch."
Character comedy also gives Enfield the licence to go more over-the-top than a Murray Walker commentary. "When you've got someone else's face on," Linehan continues, "you can afford to make him look incredibly grotesque and stupid. You don't have that chat-show thing of having to play yourself, wear a suit, and be clever. That's one of the freedoms character comedy gives you."
Enfield is as entertaining off-screen as he is on, likely at any moment to jump up and do a wicked impression of Ben Elton or Rik Mayall. Casually dressed in a zip-up top and jeans and smoking his way through a packet of Silk Cut, he defines the sort of character that appeals to him as "a strange person, out of sorts with the world around him".
A self-confessed worrier - he says that at rehearsals he is "a difficult bugger" - Enfield is constantly anxious that the inspiration might dry up. "At the end of every series, I think I won't do any more," he avers. "But as long as I can think of fresh stuff, I can keep going. When I come up with a character, I know how he lives and breathes."
He has been working on a "Dad's Army football sitcom" with long-time collaborator Paul Whitehouse and enjoys developing characters in longer vehicles as he did with his spoof luvvie, Norbert Smith, and his superannuated DJs, Smashy and Nicey. "I'd like to play a larger-than-life character done straight, like Clouseau," Enfield muses. "To move away from Dick Emery and towards Peter Sellers."
But he knows that for now overtly "challenging" material is not for him. "I'm a political person," he avows, "but I don't do much politics in my comedy. I'm a populist. People come home from a hard day's work, and they want to shut off and relax. If it's a comedy, they just want to watch it and forget everything."
Enfield cheerfully admits that he has long passed the stage of being a cutting-edge comedian. "I'm starting to get accused of not being hip," he laughs. "I'm not like Steve Coogan or The Fast Show or Vic and Bob, which are all quite Loaded shows. I want a family rather than a niche audience. I get more of a kick out of people saying, `You were in our drawing-room last night, because you've got our kid or our mother exactly.' I want the same people who watch Gladiators or Noel's House Party. I don't think you can be hip when you're 35. It's a bit sad if you think you can."
"Harry Enfield and Chums 1997" is released on BBC video on Monday.
THREE FAVOURITES KILLED OFF AT THEIR PEAK
1. Stavros The goofy Greek kebab-shop owner is Enfield's "all- time favourite". "He was fun and easy to do. And you could get the words wrong. I could call Mrs Thatcher, `The Ironing Lady', and it meant so much."
2. Smashey and Nicey Has-been DJs at Radio Fab FM. Why did they go? "It was boredom," Enfield recalls. "We thought, `we've done this'. Anyway those DJs were starting to leave Radio One and being replaced with younger, duller clones."
3. Loadsamoney. The ultimate 1980s zeitgeist creation. Enfield had him run over during Comic Relief because "he was so one-dimensional, there was nothing else I could do with him".
1961: Born in Horsham
1960s: Brought up in Billingshurst, Sussex
1970s: Studied at York University
Early 1980s: Spotted in revue at Edinburgh Festival and recruited to write gags for radio 4's Week Ending. Supported by Manpower Services grant, performed his impressionist's act on comedy circuit
1985: Producer John Lloyd scouts him for Spitting Image
1986: Invited to appear on LWT's Friday Night Live, where Stavros, Loadsamoney and a star called Enfield were born 1989: Hour-long special as aged super-luvvie Norbert Smith, being interviewed by Melvyn Bragg
Early 1990s: Two not very successful ITV vehicles, Gone to the Dogs and the first series of Men Behaving Badly
1992: The Harry Enfield Television Programme which became Harry Enfield and Chums in 1994
1993: Harry Enfield's Guide to the Opera on C4