Miranda Richardson likes complicated characters. It's appropriate, says Genevieve Roberts, because she is one herself

Miranda Richardson is a private person, and while she accepts the trappings that go alongside being recognised as one of Britain's best actresses, it seems that if they were not "part of the deal", she would not seek out the stress of festivals or attention in the street.

Her apparent lack of showiness serves to emphasise this; it is only as she speaks, occasionally clicking her tongue and giving an expansive eye roll, that the expressions on her face reveal Miranda-the-actress, who can transform herself into tabloid temptress, wronged wife or fragile murderer with a glance.

On camera, every emotion registers across her face with intensity. But in person, she is guarded, almost elusive, entertaining yet not wholly relaxed. She shares her home in the West Country with two dogs, two cats and an axolotl, whom she misses when she is filming abroad. "They're family, you worry about them."

Even so, the month she spent in Swaziland, playing Richard E Grant's mother, characterised as Lauren Compton in Wah-Wah, the semi-autobiographical tale of his childhood, was "great". She loved working with the cast, many of whom she had met on films previously. Gabriel Byrne, who plays her husband, was relaxed, a very different person from the remote man she had met on Spider, "which we laughed about, and of course he says the same about me."

The film, Grant's directorial debut, charts his father's descent into alcoholism after his mother has an affair with her husband's best friend. Richardson relied on Grant to be "his own best shit-detector" and his latent compassion for his mother comes through in her characterisation. "If you don't understand her a little bit, you are on a hiding to nothing, because you think she is an evil cow completely, and we can just boot her out the picture," she says.

Though Richardson did not know the minutiae of Grant's life before working on the project, she says he is a "great talker" - a description that is less apt for her. She has been said to be prickly in interviews, but this is more a combination of natural reticence and conversation that is anything but glib, made up of staccato thoughts and half-thoughts, which she seems to measure as she speaks.

During lunch in a Notting Hill restaurant, she talks passionately about her love of birds of prey, about the con of celebrity, and about teenage crushes (Richard Harris and John Wayne: "A very strange crush. I'm over it now, it's OK, but I did get his autograph") and how she would love to work on a "spankingly written" romantic comedy.

I meet her hours after she has flown in from Ireland, where she can mostly wander around anonymously. "It's just good for your head, it's good to be able to think," she says. She is playing the character of Mabs in a film based on Fay Weldon's novel Puffball. Work keeps her going "mentally as well as financially", but she sounds surprised when I say she seems to be very busy. "Do I? I think it's mainly stuff that I've already done, this is the first one this year."

Only once, when I ask about marriage, does she sound defensive, saying she would rather not venture into such personal subjects, though she adds: "I think marriage would be quite good for me, but I'm not just going to go out and hire somebody."

Richardson grew up in the coastal town of Southport, though her neutral accent has no trace of the North-west. "You could never find the sea, it was never in," she says. "There were lots of dead jellyfish and a pony and cart going along digging for lugworms, a bit grim." After studying drama at Bristol Old Vic theatre school, her first major film role came at the age of 27 when she played Ruth Ellis in Dance with a Stranger.

She turned down the role in Fatal Attraction that Glenn Close played, and instead became the head-chopping Queenie of Blackadder. "People love it still, so I'm very grateful," she says. "I somehow managed to be on the fringes of comedy, without having the dreadful responsibility of being regarded as a comedian. I love being inveigled into comedy."

When I say I've read that she became depressed after playing the role of Ellis, she replies drily: "I think partly why I got depressed after Dance with a Stranger is that it was very hard work and I didn't look after myself. It's a bit like the Tom Cruise syndrome of exercise and vitamins, it's all you need. And maybe in that case it was all I needed, but I didn't know that then."

But she learnt from Dance with a Stranger that she doesn't think it's great to do dark all the time. "For instance, if you have dark going on in your life, everyone would naturally assume that would be the time when you would do dark brilliantly, but I think the opposite is true, actually. It's almost like you're a bit numb, you don't manage to access anything. Do comedy, change the molecules around a bit." She has looked for roles that give her "something to kick against", though she says "big, crappy" films have their own challenges.

She loved playing the tabloid journalist Rita Skeeter in Harry Potter and the Goblet of Fire. She combined elements of the Vivienne Westwood of yesteryear with "someone like Liz Smith", gossip columnist for the New York Post. "Kids are very generous. I got some really sweet letters saying: 'You were exactly how I thought you should be', so I was very relieved about that," she says.

She is attracted to complicated characters, such as Stella in Stephen Poliakoff's recent television drama Gideon's Daughter, and lets herself morph into a character, rather than coming up with a list of props. "I don't automatically go for show and false noses, I kind of do it from inside out," she says. Is she referring to Nicole Kidman, and her prosthetic nose, as Virginia Woolf in The Hours? She laughs: "I wasn't, actually. I know you're not going to believe that, but I was thinking Laurence Olivier."

But Richardson felt unsettled working on The Hours [she played Woolf's sister]. "I felt very distanced from the whole process, which was only about eight days on the shoot. I didn't feel happy in what I was doing, in the way I looked, in my day to day on set, and I cannot help but feel that comes across, that's all."

She has two films premiering at this year's Cannes film festival, Paris Je t'Aime and Southland Tales. The former is made up of five-minute films strung together, all from different directors and different actors, one for each arrondissement of Paris.Southland Tales, written and directed by Richard Kelly, has an "extreme" cast, including Justin Timberlake, The Rock, Sarah Michelle Gellar and Wallace Shawn.

Directing a short film herself is something she has thought about. "I love the idea of doing it with a group of friends, gather people around you who if they're not working, they should be working, and if they are working, you drag them in when they're not working. And just do something you really want to do. That should be the impulse behind it all. Though it doesn't work like that most of the time."

'Wah-Wah' opens on 2 June