Do you mind being porky? No, it’s fun. I like being able to transform myself. That’s part of the thrill of being an actor.

So have you always been delightfully svelte? I’m a perfect genetic mix between my voluptuous mother and my thin father. My mother’s the archetypal Jewish mother. At the first sign of a cough she’ll rush round with chicken soup. Chicken soup has been the cure-all for me; it’s my comfort food, my treat, my penicillin.

What else makes your mouth water? I love sushi and salads. I can eat anything, but I guess I am lucky that I’m not fond of greasy fry-ups. That said, I have to be very disciplined about what I eat. Being on stage is like having an exercise regime — you have to eat the right foods to cope with the adrenalin rush each night.

How else do you burn up energy? I live on the top floor of a building with no lift and run up three flights of stairs five times a day. I’ve lived there for years and that’s usually enough. I always forget that I have to offer oxygen to people visiting me.

No other exercise? I’m shambolic, I can never stick to anything. I am completely addicted to Bikram yoga, though. You do the same 22 poses in the same order so you can monitor your progress and I like the fact that you get results quickly. With other types of yoga, you just work on one pose for an hour and I never really feel I’m tracking my improvement.

Actress + pretty = vain? I’m absolutely rubbish at any type of grooming. You read these articles where women say that they have a facialist, manicurist, waxer and a plucker. Who are these people and how have they got the time and money?

You mean you do nothing? I’ve got one beauty tip. I used to live opposite the photographer Terence Donovan and one day I asked him why he was taking crates of sardines out of his Bentley. He told me that he’d met a scientist who’d made millions from a beauty treatment that was basically fish oil. So I eat oily fish every day.

Pop any pills? Only the homoeopathic kind. I suffer dreadfully with my sinuses. Every time I catch a cold I get a sinus infection, which means the cold lingers for ages. As you can treat the infection only with antibiotics, I’ve resorted to homoeopathy.

Are you a convert? Absolutely. I also make lots of recommendations to friends. If they’ve just had a baby I show up with arnica as a post-operative remedy; I take caladium for sinus problems and arsenite is a great treatment for stage fright.

Is that something you are afflicted by? Everyone suffers at some point. At the start of a play you’re working really hard, rehearsing all day long, then there are technical rehearsals under the lights and, finally, the opening evening. Just the stress of it puts you on edge. I’m not someone who naturally suffers from stage fright but I can become overwhelmed.

As you grow older does it become worse or better? You lose the fearlessness of acting as you get older. When I was young I looked at the older actors on stage and wondered why they were shaking. Now I understand; every time becomes the first time.

What’s the cure? Well, I’m perpetually trying to kick the smoker’s habit.

Have you been an addict for long? I started when I was really young and for the past five years I’ve been pretty much on and off. At the moment I’m on. It’s definitely stress-related, not a social thing. Last year when I was travelling I didn’t smoke at all. Now that I’m auditioning I’m puffing away.

So being an actor is bad for your health? No, there is such a great element of play in acting that most actors are pretty laid back and have great skills at being able to switch off stress. There’s an element of fun in almost everything I do, whether I work or play. I like that element of Jane in Coupling because I consider her to be very playful.

So what’s the downside? The nocturnal lifestyle. When you come off stage you need to unwind and that’s usually in a pub with a few drinks and some packets of crisps.

Interview: Kieran Falconer

Insignificance is at the Royal Theatre, Northampton, from April 23; 01604 624811

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?