Most dancers of her age have long ago folded their hands and retired, but Seymour still, doggedly, makes a dancing life for herself. Not only does she teach, coach and occasionally choreograph, but she also continues to perform, in roles that lie way outside the usual dowager repertoire. She appeared in Derek Jarman's film Wittgenstein; she created Lowry's mother in Gillian Lynne's ballet A Simple Man; and she's currently performing in a new production by the experimental dance theatre group Second Stride.
Escape at Sea is partly inspired by Chekhov's The Seagull (Seymour plays the ageing actress Arkadina), but it also uses other texts, as well as song, dance and image to create a free-wheeling fantasy about exile and loss. If it's anything like past Second Stride productions, it will be dense, allusive, stylish - and either wildly stimulating or infuriatingly chaotic.
The director Antony McDonald knew exactly why he wanted Seymour. 'She's a great dramatic dancer, she's brave and she's vulnerable.' Seymour herself, though she knew nothing about Second Stride's work, jumped at the chance. 'It's always thrilling to be asked and doubly, trebly so because it's not often someone my age gets to do a created role.'
When we spoke, Seymour was only two weeks into rehearsal. Among the other dancers - still in drab woollies and battered sweat pants - she was certainly unmissable. The tinted glasses and the little lap dog trotting at her heels shouted 'star'. But the jaunty red cap, the vast ruby glass brooch made by her long-time friend and collaborator Andrew Logan, sent out different signals.
In fact, Seymour even at her starriest was always a maverick. She never made a secret of her volatile private life, with its succession of short-lived relationships and occasional bouts of depression. And for all her critical successes, her relations with the Royal Ballet were erratic. As a Canadian, Seymour felt an outsider when she first entered the company and that feeling persisted: 'I was never terribly happy in a large institution.' She felt, too, that her talents were under-valued, and after each spell away from the company (due to brief contracts with other companies, child-bearing and illness) she found that her welcome home became less warm. After she'd cancelled her final comeback as a guest star in 1981, she gravitated more and more to the world of fringe film and theatre, fashion, and modern dance. She's thus quick, almost defensively quick, to say that working with Second Stride is 'not like I'm plunging out of a tutu and into the realm of modern dance. I don't feel like a fish out of water, just a bit old.'
The first rehearsals were 'agony', though. 'I hadn't done any dancing for quite a time and just being on my legs all day was hard.' She talks about her body with a mixture of impatience and concern, as if it were a reluctant child. 'At the beginning it just went 'help, help'. But it's had to make a lot of comebacks and in the end it seems to quite enjoy it.'
The choreography Seymour will dance is hardly classical. 'I can't describe it,' she says. 'Some is quite extravagant, some quite minimalist.' But that holds no terrors for her. 'What frightens me is that we have some sections of speech. I've done some speaking twice before and it scared me half to death - because you know one's not practised at it. But risk has always been my raison d'etre for slaving away. It wasn't doing a million pirouettes or being Aurora. It was because I loved creating.'
Certainly, Seymour has had her share of that, becoming Kenneth MacMillan's first dance muse at the time he was inventing a new language and a new terrain for British ballet. She was cast first in The Burrow (1958), a Kafkaesque study of terror and claustrophobia, then in The Invitation (1960), a grisly story of rape. Unlike some of the more cloistered members of her profession, these works didn't offend Seymour's notion of classical propriety. 'I just took it all for granted. I'd seen Osborne's plays, nouvelle vague was just coming out of the cinema. We seemed like part of all that: I just felt, 'Yeah, let's go with it.' '
Ballets like these established Seymour as a rare dance actress, capable of an extraordinary rawness and commitment on stage. She wasn't afraid of looking ugly. In her most famous created role, Juliet, audiences were often seriously alarmed by the retching nausea with which she swallowed her fatal sleeping potion. 'I suppose I just had a good imagination.'
But she also had beautiful feet; a lavish, rich-toned style and instinctive musicality - qualities she brought to the stricter classical roles. 'It's awesome attacking those things. You know that struggling towards them is going to enhance all the other things you do. But at the beginning, I found them very frightening. I was such an unathletic dancer. I didn't have that kind of wiry, steely strength.'
What helped Seymour overcome her fear was starting out with the Royal Ballet's touring group, where she was given many more performances than dancers in the main company. 'If you did a miserable performance, you could always redeem yourself two days later. You had time to get your stage sense and your stamina together. Kids today just aren't given enough performances or enough preparation time.' It was the lack of preparation and encouragement that made Seymour cancel her last comeback with the Royal Ballet. But she also found it dispiriting that she was only given roles that she'd created years before. She is terribly proud that those parts are hers, that she holds their history in her body. But while she's happy to coach others in them (when there is sufficient rehearsal time), she dislikes 'dwelling on the past. I've been there, I've done that. I prefer to do new stuff.'
Which is why she's now working for peanuts, and about to appear at the distinctly non red-plush Place Theatre in London. McDonald says that Seymour is a revelation in Escape at Sea - 'a real inspiration to the other dancers'. Seymour herself, looking gallant, tired and a little self-mocking, puffs on a final cigarette. 'You know, I'm terribly gung-ho. I'll go for anything. I'll hurl myself at trees, stand on my head, do anything.'
At the Place Theatre 5-7 November (Booking: 071-387 0031)