Why a week is a long time in theatre as well as politics

Indeed, Quigley will seize the reins of power as Fiona in Spoiling on referendum night itself. It's just that, being a familiar face off the telly in primetime comedies like Chewin' The Fat and the Karen Dunbar Show, Quigley gets to chat to taxi drivers a lot. In the current climate, there is pretty much only one subject that comes up.

"I'm doing a secret survey," deadpans Quigley, spilling the beans that YouGov and co have unilaterally failed to take into account. "Black-cab drivers in Edinburgh and Glasgow are Yes," she reveals, "whereas mini-cab drivers in Edinburgh and Glasgow are No. What's that all about?"

The answer may not be found in Spoiling, but McCann's look at some of the compromises that may have to be made, once the champagne corks have stopped popping for whoever wins the vote and the hangover kicks in after September 18, is as up-to-the minute as it gets.

"It's just so topical," agrees Quigley. "Doing Spoiling during the Fringe, because of the things the play's looking at, there was a wee frisson every time we did it. I think it was one of the best reactions I've ever seen at the festival. People watching it seemed so excited and happy that they were being addressed, even if they didn't agree with it. People from both sides of the argument seemed to enjoy it."

Much of this, one suspects, came from Quigley's performance as much as McCann's script, and the way she deals with the Northern Irish civil servant tasked to keep her on-message.

"She's a brilliant character," says Quigley. "She's pregnant, so that's very freeing, because the guy who has been sent in to keep an eye on her can't touch her, even though she's just been caught smoking. She's a classic politician, because she's got so many characters within her. She's a child and can be really irresponsible, but then she can say all these important things.

"People like Fiona are absolutely ego-maniacs on a power trip, but Fiona is a clever lady, and she does mean what she says. She's passionate, and goes 0-60 in seconds, but can be quite hard as well. There are obvious shades of Peter Capaldi as Malcolm Tucker [in The Thick Of It] when she starts swearing, but Scottish people swear very well."

If there are shades of the late independent MSP Margo MacDonald's fiery spirit in her portrayal of Fiona, Quigley has also been referring to the flamboyant late Conservative MP Alan Clark's somewhat scurrilous diaries to see just how badly behaved politicians can be. It is MacDonald's influence, however, which remains close to home.

"Margo was in the swimming team with my mum," she says. "They went to different schools, but my mother was brought up in Hamilton, and they were both very blonde and very glamorous. They weren't afraid to be feminine, but they were very strong as well. My mother was a midwife, and there was a campaign for midwives which Margo MacDonald supported, and my mother always remembered that."

In many ways, playing Fiona seems to encapsulate all the different facets of Quigley's two-decade-long acting career, which has seen her play broad comedy with an intelligence that imbues it with a seriousness others might miss. Much of this, one suspects, stems from Quigley's background in Hamilton, growing up as the youngest of six in a highly politicised household where her teacher father would lap up piles of daily newspapers from all sides of the political spectrum.

Quigley originally planned to become a journalist when she studied English at Glasgow University, but falling in with a crowd from the Theatre Studies department that included playwright Nicola McCartney and future Black Watch director John Tiffany soon put paid to that. Quigley appeared in McCartney's student production of Arthur Miller's Death Of A Salesman, and in a double bill of plays presented by McCartney and Tiffany's newly formed Lookout company.

Her second job was a tour of Trainspotting at the height of Irvine Welsh mania alongside a cast that also featured Billy Boyd. "I went to quite a rough school," Quigley points out, "so I ended up playing a lot of people like that."

Quigley's career has seen her work mainly with new writing, including a Herald Angel-winning turn in Rona Munro's translation of French romcom, Strawberries In January. She later reunited with Tiffany for Enquirer, the National Theatre of Scotland's timely verbatim study of the newspaper industry's fluctuating fortunes. Quigley most recently appeared in Tomorrow Is Always Too Long, a film by Turner-nominated artist Phil Collins, which was recently shown at Queen's Park in Glasgow.

It is Spoiling, however, that is the most relevant play around. During its London run, Quigley has noted marked differences in the audience's response. At the start, she observes that the referendum debate had "barely touched the surface. There was no real sense of what was going on."

A week and a half later, and Fiona's speech about how the referendum would affect Northern Ireland was interrupted by an audience member loudly disagreeing with it. The day after a post-show discussion, and the change is even more marked. Quigley describes the audiences as "stricken" in their need to understand exactly what is going on. In a lively sounding debate, a group of young people in the Stratford East audience asked about the National Collective, the pro-indy artist-led collective they'd discovered online. Others too were hungry to hear what was going on in Scotland,

"The difference in a week is remarkable," says Quigley. "It's just hitting home to people in London how much this matters. On one level, Spoiling is a popular comedy, but if it's having that effect in London, it shows just how much something is happening."

Spoiling, Theatre Royal Stratford East until September 13; Traverse Theatre, Edinburgh, September 16-20.

www.stratfordeast.com

www.traverse.co.uk