Kendal is happy to talk about it. "They haven't come off till now because it hasn't been necessary or appropriate. It's not because I've at last been asked and I've been dying to do it for all these years," she says in that smiley, throaty voice that swells into a giggle which is something between a coo and a gurgle and then explodes into a gleeful, slightly wild "ha, ha, ha". Then, in an instant, she gathers herself together and is once more all no-nonsense composure. "It was always a decision. I'm not a great flasher obviously, but I'm not a shy person either. I didn't think twice about it, possibly because it's to do with Flora's illness and isn't something that tries to be sexy. The play's about a guy painting a woman nude. You'd be selling it short if you started being coy. If there's one word you don't want to read about this character in a review, it's coy."
On reflection, this is the one stage direction we should perhaps have predicted in a new Stoppard. For years he has been writing roles apparently designed to show Kendal in the most delightful light, and to reveal outer as well as inner perfection at the age of 48 is just another accolade. It is safe to say that Kendal is never going to appear in a Stoppard wearing a filthy slip, her hair greasy, throwing herself at a passerby. She says this is nothing to do with her, everything to do with what he writes.
"Tom doesn't write character plays, he writes about ideas, more like Shaw really. He likes writing clever people. The characters could swap some of the dialogue because they're presenting this magical circus of links and loops and language. You can't push too much blood and guts and sweat and deodorant into his plays because they're not about that."
This is Kendal's sixth Stoppard (six and a half if you count the radio play In the Native State which is the source of Indian Ink). He was so determined that this "bossy little blonde ", as he affectionately described her, should premier Hapgood that he delayed the opening to fit in with her second pregnancy. So is she Stoppard's muse?
"I know what you mean," Kendal says. "There's obviously a link, but three of the plays have nothing to do with me at all. I've absolutely no idea how anyone writes anything but I'm sure it always is related to the people you know. It's a partnership that works - it's like a painter finding the kind of shape he wants in a woman, a building, a landscape. That is what you are; you happen to be it, but you don't make it. There are people that influence people but it's only because they fit." Fluffy she may be, but she is also extremely firm.
She met Stoppard for the first time when she was cast as a boy in On the Razzle in 1981 at the National ("my most favourite part in the world") while she was doing Othello and Amadeus. They became a rather glamorous couple, but The Real Thing had been written before that, so had Arcadia - and the production of Jumpers she was in was a revival. This leaves Hapgood, Native State and Indian Ink (the two latter set in India, a background shared by Stoppard and Kendal) as the only plays in which she might have had a direct influence. There are few people with much clue about the terms of a partnership conducted from separate Chelsea houses: "The relationship we want works wonderfully. What it is is my secret, and one day I'll write a book about it." Kendal goes to some pains to establish how single she is right now, explaining, as she removes a large pair of boots from her drawing room, that her eldest son, Charlie, is very happy to live at home because there is no competition for who's going to sit in the most important chair. She also insists that Tom's plays would be written and staged whether she was around or not, and that working with him might not be everyone's idea of fun. The play opens tonight and he has been madly shuffling scenes and reworking the end.
"It's tricky when things change because I like practising. I'm not one of those actors who turns up with a performance. I put it together bit by bit and find out how I like to do it. I'm entering the phase I always reach around this time when I want to shout `Taxi!' and go somewhere else and not do it." She won't, of course, and despite last-minute alterations she will pull it off. Kendal has a reputation in the business for commitment, competence, great charm and a natural sense of timing.
Today she is wearing tiny tight black jeans and a classy gauzy jumper designed to reveal a tiny sleeveless black body beneath. She perches on a stool, legs astride, one elbow on one knee and her chin cupped in her hand looking every inch (5ft 2in, size six) like Peter Pan. The part of Flora requires her hair to be English mouse - "Not being blonde is a much bigger sacrifice than taking my clothes off" - but apart from that and a faint line or two, and minus the cardy and wellies, she's instantly identifiable as Barbara in The Good Life, a part she played two decades ago for eight years. "She was gutsy, not too glamorous, absolutely devoted to her husband. Everyone's perfect partner. It's a winner, that kind of part." A survey done at the time revealed that half the male population was secretly in love with her, the other half made no secret of it. She hopes they will come to the play, but suspects that the cost of the theatre ticket might well test the strength of their infatuation. "If you charge 50p an autograph, you suddenly find people don't want it quite so much."
Despite a recent hilarious appearance on Ruby Wax wearing a bustier, thigh boots and cracking a whip ("I got a completely different reaction from the boys in Peter Jones the next day") the squeaky-clean image of goody-goody Barbara sticks like marmalade, and she doesn't ever expect to shrug her off entirely. In any case, she offered her the break she badly needed.
Kendal has no classical training. She was brought up in India where her parents, actor-managers, went with Ensa during the war to tour doing twice- nightly rep. They fell in love with the heat and the jasmine and stayed for ever. If one of the troupe died, they wired Spotlight in London to send someone new. At the age of 10, Felicity was an accomplished stage manager, had played Puck and knew most of Shakespeare off by heart. "It was a wonderful apprenticeship but no one was very interested when I came back to England. It was all Julie Christie and Twiggy, and it was terribly hard to get started."
Her biggest fans - Peter Hall among them - will cast her adventurously, encouraging her to play down the doll-like vulnerability and turn up the forcefulness in parts such as Desdemona. "He made me much stronger. I found it quite hard to be anything other than reasonably pleasing until then." For her unremittingly tragic performance in Ivanov she won an award, and yet she has rarely been given the parts of deeply suffering souls. One critic has suggested this is because she is always Felicity Kendal her suffering is not plausible. "You can't expect the praise without also expecting the damning, and you have to be brave enough to try things. The instrument I have won't fit anywhere. I've done parts which I feel someone else would have done a great deal better but you just struggle on."
She is sorry she's missed out on some Shaw and some Shakespeare she now feels she's too old for, but there's "lots left to do that's quite yummy and the experience I've got is really nice to have. I simply enjoy working. For all one's pretensions to being artistic and clever and good, what's really lovely is being in a short play with your chums that goes well, and then you go home early."
`Indian Ink' opens tonight at the Aldwych Theatre, London WC2 (0171- 416 6003).