Everything she does seems to be infused with this sense of relish. Whether teaching drama, playing a vicar or giving an interview, she fills the space around her with her ebullience. You feel that she would view a visit to the dentist as a laugh - or at the very least as fertile material for a sketch.
She and her long-term partner Jennifer Saunders have long been the golden girls of TV comedy - ever since they starred in Five Go Mad in Dorset on Channel 4's very first night. Recently, however, some critics have gone against the comic orthodoxy and committed the near-blasphemy of attacking them. The last series of French and Saunders was castigated for its perceived self-indulgences and for the length of some its sketches.
"Plenty of critics said that we were dirty, slaggy whores who have no talent," French avers. "And if you're to believe the press, everything on the last series was too long. But we're on a mission to do characters that last a while, and they're harder now that our culture is so soundbitey. Much as I love things like The Fast Show, I'm worried that everything might just be quick catchphrases. But out of our 12-minute characters came Absolutely Fabulous. That was a big long sketch, and it didn't really go anywhere. It was just about some people. We do quite a lot like that."
Another charge levelled by critics is that the series now relies too heavily on parodies of other TV shows and Hollywood movies. Again, French mounts a stout defence. "That's the joy of doing our show. We watch a film and go, 'Hooray, I can't wait till we can have a go at this.' When we see Braveheart, we think, 'Great, we're going to get to go on horses.' It was ripe for us. It's not great political satire."
French's nonchalance is perhaps not surprising. After all, her partnership with Saunders has been through worse than the huffings and puffings of the critics. In fact, they've survived the greatest test known to showbiz duos: solo success. "I was completely eaten up with jealousy about Ab Fab," French concedes, though she too scored a ratings hit with The Vicar of Dibley. "But actually I'm more proud of her and happy for her than I am jealous of her. We've got kids that are more important [French and husband Lenny Henry have a four-year-old adopted daughter called Billie]. You can have flashes of fury, but friendship is more important."
Now they've reached a point where, according to French, their solo projects are "absolutely vital to our particular relationship. We're always happier if we've been apart. It's like you go off and have an affair with someone else for a little while, then you come back ready for your old partner. It just spices things up. You can get too insular and self-absorbed if you're working with the same person all the time."
From the moment we meet, in the lounge of London's Kensington Hilton, French is a barrel of laughs, complaining about being knocked off the cover of the Radio Times by a fly from a nature programme; and getting into a mock-schoolgirl row with the PR over whether the AA or the RAC is better. Even her trousers - sporting a loud red tartan pattern - are jolly.
Liberally flashing her immaculate white teeth, she takes a great interest in other people. She solicitously asks me about my family and checks I haven't left my bag when we leave. This attention to others undoubtedly contributes to her talent for conjuring up characters. From French and Saunders, think of the two (male) sexist slobs who lounge on a lager-strewn sofa and go "phwor" at the Queen's Speech; or the two impossibly hearty country women who dismiss the loss of limbs in agricultural machinery as so much "stuff and nonsense". These are comic exaggerations with a firm root in reality.
So how has she developed her keen comic eye? "Off screen, Dawn's always very nosey about everyone's personal life," says Sophie Clarke-Jervoise, the producer of Murder Most Horrid, the series of comic mini-dramas about killing which starts a new run on 10 May. "She makes sure she knows everybody's name in the crew. She's very observant and that comes across in her work. I watch her characters and I think, 'Yes, I know that person.' "
French also has a surprising range as an actress. She plays six very different characters in Murder Most Horrid - everyone from the Grim Reaper to a super-efficient PA - but she has also made her mark in a straight role - as the murderous nurse in Lucy Gannon's TV film, Tender, Loving Care. Jon Plowman, who has been producer or executive producer on all her work since 1988, ascribes her acting skill to "Nous. Dawn has an instinct about judging a performance. She thinks to herself, 'If I go too big here, they won't buy it, and if I go too small, it'll get lost.' It's a question of seizing the moment."
The creative process itself is far from glamorous. French and Saunders sit slaving over a hot keyboard for months on end. "Often we think of the characters, and we become them for a while," French reveals. "It's not something I'd ever want anyone to see. It's totally and utterly humiliating to try out jokes you think are funny and then to hear the other person say, 'I think not.' If people think that the sketches are long, they should hear the improvisations."
She and Saunders have been parodying people since they met at London's Central School of Speech and Drama in 1977. Born in Holyhead 38 years ago, French was sent by her RAF-pilot father to St Dunstan's Abbey in Plymouth, the girls' boarding school. She went on to take the drama-teaching course at Central, where Saunders was a fellow student. They took great pleasure in sending up the earnestness of the drama students at the end- of-term revue.
When they left, French diligently took up that job at Parliament Hill School for Girls, while Saunders "drank champagne and did the Times crossword". After answering an ad in 1980 for women comedians at the Comic Strip, they became regulars, alongside Alexei Sayle, Rik Mayall and Adrian Edmondson (later to become Saunders's husband). Taking Sayle's advice, they decided against the stage names of Kitch'n'Tiles and went for French and Saunders instead. Without even realising it, they were riding the crest of the alternative-comedy wave.
When the offer of a Comic Strip tour to Australia came up, French threw in the chalk in favour of greasepaint. By 1982, the Comic Strip were making TV films. After two series of the sitcom Girls on Top in 1984-85, which they made with Ruby Wax, French and Saunders made the first (of five) series of their eponymous show for the BBC.
The closest French gets to serious is when the issue of fatness looms into the conversation. Two years ago, she made a South Bank Show and posed nude for Esquire to make a point about the desirability of bigger women. A size 20 herself, she has opened a shop in north London for the more generously proportioned woman. "How can you have any confidence, how can you get on with your life if you can't get dressed?" she asks. "We've had women in our shop in tears because they've found a pair of trousers that fits. There's a tyranny of thinness."
French has also been seen as a missionary for women in comedy - a part she is less comfortable playing. "At the Comic Strip we became role models for women, but there was nothing Boadicea-like about us. We were just lucky. Spare Rib attacked us for not being positive enough about women in our sketches, but we never set out to do anything like that. As far as I'm concerned, the equality for women came in making them as ridiculous, as absurd and as pompous as men."
She is currently working on a screenplay (subject undisclosed) and preparing to appear this summer in Jude Kelly's production of Now We are Married at Chichester. With a five-year BBC deal in their possession (reportedly worth pounds 2m), she and Saunders are in an enviable position of power. "Nobody tells us what to put on the screen anymore," she says. "Any mistakes you see are totally down to us.
"What better job?" she wonders, gleefully. "Dressing up, showing off, being with all your friends and getting paid for it. I can't believe I'm getting away with it. Somebody's going to come along and arrest me soon."
The new series of 'Murder Most Horrid' begins on Friday 10 May, BBC2.Reuse content