Jessica Hynes peeps her beaming face around the Old Vic stage-door and hands me a hard hat. “Would you like to have a look inside? It’s amazing what they’re doing.” Hynes (née Stevenson) leads me up a flight of stairs into the auditorium, where carpenters are building an impressive ring of seating for the production of Alan Ayckbourn’s The Norman Conquests for which she is rehearsing. The triptych of comedies was written to be performed in the round, so some of the audience will be watching the cast from where we are standing on the Vic’s vast stage.

She gushes about the three ingeniously interlocking plays, which chart a weekend of squabbling, eating, drinking and canoodling in a middle-class English country house in 1973. “Ayckbourn wrote it in a week!” she chirps. “But when you start rehearsing it you realise how clever and complicated it really is.” She plays Annie, a frumpy young woman living with her tyrannical mother, who becomes an amorous target for her married brother-in-law, Norman (Stephen Mangan).

The plays crystallise an era when “the constraints of dutiful marriage were being shaken up”, she says. “Norman embodies the rather fumbling middle-class man grappling with these new ideas and living them out.” The original production starred Tom Courtenay, Michael Gambon, Penelope Keith and, as Annie, Felicity Kendal. “She was a lot sexier than I’m going to be,” Hynes laughs. She’s being a bit hard on herself – and in blouse and jeans, she looks younger than her 35 years.

Her emotional intelligence seems well suited to Ayckbourn’s brand of social comedy, but as she chatters away it’s impossible not to think of another of her characters: Daisy, the babbling, desperately enthusiastic would-be journalist she played in the Nineties TV sitcom Spaced.

She has had plenty of other high-profile roles – Sheryl, the butt of Caroline Aherne’s fat jokes in The Royle Family; a nurse and love interest for David Tennant in Doctor Who; the devout mum in Son of Rambow; her Olivier-nominated stage role as the unruly jailbird Bolla in The Night Heron in 2003 – but she will be for ever linked with Spaced, which she wrote with her co-star Simon Pegg. It encapsulated that twentysomething transition between student sloth and adult responsibility, refracted through a playful prism of movie, TV, and vide-ogame references.

Given her note-perfect observations of kidult life in the show, I am surprised to learn that Hynes was already a mother when she filmed the first series. She has been with her husband, Adam, a sculptor, since they met in a nightclub (“Classic!”) shortly after her A levels, and they now have three children. She changed her name in 2007 for no reason other than it felt like the right thing to do. She has fond memories of Spaced: she wrote it, like Daisy, on an old typewriter on the floor of her sister’s flat, and the cast and crew became like a family.

I ask whether she has seen the diagram in Empire magazine, which features Spaced at the centre of an entertainment universe: Pegg and Hynes orbited by their guest stars – Bill Bailey, David Walliams, Mark Gatiss – and celebrity fans – Quentin Tarantino, Peter Jackson, J. J. Abrams. She laughs nervously: “Yeah I did see that . . . It’s lovely being in such a . . . yeah . . . I did see that . . . yeah.”

We are on sensitive ground here. Spaced launched the careers of Hynes, Pegg and their director Edgar Wright. But, while Hynes’s CV since then has been more than respectable, especially considering she has had children, Pegg and Wright have graduated to big-screen comedies with Shaun of the Dead and Hot Fuzz.

Their divergent plans emerged during the second, final series of Spaced. “The idea was that they would move on with the production team and do Shaun of the Dead, which was going to be written by Edgar and Simon. And not me. I was playing the ‘That’s fine’ role because I was hurt, but I didn’t want to be a girl about it.”

The shift was reflected poignantly in a scene in Shaun of the Dead in which Pegg and co come face to face with their doppelgängers, one of whom is played by Hynes. From creative pillar to bit-part lookalike.

She shuffles in her seat and her eyes moisten. “Can you imagine after Spaced if I had gone and written a film with Edgar and written a part for Simon in that? How might he have felt? How would you have felt?” Sad, I say. “Yes, I was very sad. Literally, on a physical level, I loved Simon.” She’s using the past tense, I point out. “I’ll always love them. But it’s not a live thing because they’ve gone to a different creative place.” The geek-friendly, arguably less character-based route Pegg and Wright have taken is “great fun, but it’s not necessarily what I would have wanted to do. They went and did it and I don’t think it occurred to them to ask me if I wanted to do that.

“I was very sad for quite a while afterwards, and quite numb. I couldn’t get my head round it.” It was a while before they were in touch. “There was a bit of tension, a bit of: ‘Why are you being like that?’ ‘I’m not being like that’ and that creates a distance which then becomes a chasm.” They now e-mail occasionally. “I see Simon like a distant cousin or something. I don’t care what s*** goes down. I will always be Simon’s friend because that’s how I am,” she adds.

Hynes seems on the verge of tears but she keeps it together. She is anxious that she doesn’t come across as “a bit of a sad-do. If there’s one thing I can’t stand it’s self-pity.” The ability to bounce back from adversity – another classic Daisy trait. “Absolutely,” she says. “I’m a very resilient person.”

Some of that resilience, she thinks, is tied up with her “passion and joy for life”; some is inherited from her mother, who was left to bring up Hynes and her sister when their father walked out. She grew up in Brighton, where her mother surrounded her with a Bohemian surrogate family of “really interesting people” including a tattooed blues musician. The emphasis was on authenticity: “You couldn’t be a fake.”

Truthfulness is still key. And, while she would “still be the butt of fat jokes for Caroline Aherne at the drop of a hat” there is a new assertiveness. She recently waded into the bear pit of stand-up: “I don’t think I was very good but I absolutely f***ing loved it.”

There is also a new, unnamed, TV series for the BBC with her new “comedy playmate”, Julia Davis. She and the Nighty Night creator have already collaborated on Peppatits, a series of podcasts for Resonance FM. “It’s comedy improvisation. Some of it’s very dark.” As will be some of the TV series, which is being produced by Steve Coogan’s Baby Cow company.

Working with Davis has reminded her of Spaced. “We just started mucking around together. That’s one of the things I miss most of all from working with Simon.” There is no hint of tears this time; just smiles. “I feel like I’ve got to the bottom and . . .” she stumbles around for the words. “It’s like suddenly coming out of the undergrowth into a clearing and going: ‘Great! Brilliant!’ ”

The Norman Conquests, Old Vic, London SE1 (www.oldvictheatre.com 0870 0606628), from Thur until Dec 20 2008

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