Side by side

Teetering precariously, Ferguson draws herself up to her full height – about six foot three in her sexy shoes – and says: "Aye, well I cannae walk in them either. I only wore them for the photies because I didn't want to look like a big German lesbian."

At this, Ash creases up with laughter and splutters: "You look nothing like a big German lesbian, Lynn. You're more of a Brigitte Nielsen."

"Aye, exactly," counters the award-winning Scottish actress, stand-up comedy star, playwright and mother of two small sons, running her hands through her shock of white blonde hair so that it stands spikily to attention.

"German lesbians look at me and they see big competition, a big, mouthy broad from Cumbernauld," Ferguson continues, before launching into a riff about the post-natal benefits – she had her younger son, Lachlan, a year ago and has a five-year-old, Fergus – but slightly humid nature of big pants. "They are bloody brilliant," enthuses the 44-year-old, who is preparing to return to the Edinburgh Fringe with two solo plays. "They're holding everything in – and I do mean everything.

"You just hook the pants onto your bra and they go all the way down to here," she says, pointing to her knees. "Have you no' tried them?" she asks me.

Ferguson's surreal stream-of-consciousness has 48-year-old Ash wiping away tears of laughter. It's a moment that sums up their affectionate personal and professional relationship.

Ferguson has neatly defused the situation for her close friend, for whom she has just written a role – "a Bliography – part biog, part blog", which can be downloaded on the internet. Ash acts with honesty and intensity in a piece about the post-Impressionist and creator of pointillism, Georges Seurat, and her own life and troubled times.

"And listen to that. Absolute silence broken by the crash of countless jaws dropping," Ash says, quoting her Bliog, which questions how any of us would live someone else's life.

Famous for her roles in Men Behaving Badly, Where the Heart Is and Merseybeat, she received a 5 million compensation package from London's Chelsea and Westminster Hospital for the "shortcomings" in her care while she was a patient there. But she would forfeit that just to be able to walk without the aid of a stick, she says. It's an elegant stick, mahogany with a silver handle, and it cost 400.

"It's bloody expensive, but I was so pleased when I bought it. I was never going back to crutches," says Ash, the mother of Joe (19) and Max (16). "And look at me!" she exclaims, rising slowly to her feet, wildly waving her stick in the air: "This is a great way to guarantee you'll always get a cab."

It's four years since she was in hospital being treated for cracked ribs and a punctured lung after an evening out on the lash with her husband, footballer-turned-club owner, Lee Chapman. Contracting MMSA, a virulent strain of MRSA, she was left temporarily paralysed after doctors discovered an abscess on her spinal column and had to cut through two vertebrae to reach it and stop the infection spreading.

She was left with chronic paraesthesia (the sensation of pins and needles) caused by nerve damage, and was unable to feel or move her legs. Months of physiotherapy followed and she's still in pain most of the time. "If I lose the thread, it's the drugs," she quips.

We meet in a private room at the Groucho Club, in London, the media watering hole where the one-time party girl would gaily knock back vintage champagne or double vodkas, not the mineral water she's sipping today. The room is up two flights of narrow stairs, which she gamely negotiates, refusing all offers of help.

She and her husband have just returned from Los Angeles, where she has been filming a documentary for ITV about plastic surgery and the need for legislation to control Britain's cowboy practitioners. "They have such stringent laws in the States," she says. "They even have plastic surgery police in Miami.

"They asked me to do the programme for obvious reasons," she adds, referring to the botched cosmetic procedure on her upper lip that led to her infamous "trout pout" – the butt of jokes and paparazzi pictures before illness struck her down.

"Oh God, all those pictures! But my top lip looks all right now, doesn't it?" she asks anxiously, touching her mouth. "A top cosmetic surgeon I interviewed in America told me it was looking good. He said I could have ended up unable to move my mouth at all."

She's come back from LA early to do this interview since she's keen to talk about her return to serious acting, thanks to her friend Lynn.

FERGUSON HAS WRITTEN A BEAUTI- fully observed, blackly comic monologue for Ash. It can be downloaded from the internet, along with Ferguson's own mordantly funny Bliog, in which she ponders the joys and terrors of motherhood, as well as the relationships between mothers and daughters, while asking whether philosopher Arthur Schopenhauer's enthusiasm for pessimism made him happy.

Meanwhile, Ash considers the life and work of Seurat, joining up the dots of her grief at the death in 2000, at 68, of her mother, Ellie, whose family was from Dennistoun, in Glasgow.

"When mum died, everything changed for me," says Ash, "She was just fab, my mum. Always on the go, always looking fantastic, dead streetwise. She was a lovely, laughing, barrel-shaped woman, with skinny arms and a screeching laugh. She died so suddenly and that's when I started drinking, drowning my sorrows. I was lost without her.

"My parents had a painters and decorators' shop in Clapham. Mum was so popular that people like Joanna Lumley used to come in just to have a chat with her. Everyone loved her. Mum knew everything about colour – just like Seurat. When she died, it was like all the colour had been sucked out of my world. I often think about what she would have made of everything that's happened to me. It's certainly been a bit of a trial."

Those trials were the inspiration for Ash's Bliog. She was to have made her Edinburgh Fringe debut with Ferguson's Biographies in a Bag, a trilogy of confessional monologues, in 2004. "This was after the big lip event, but before the spinal thing," points out Ferguson. Struck down by the MMSA infection, Ash had to pull out and Donna Air took over.

"I was so looking forward to being taken seriously for once," Ash says.

"I still desperately wanted to work with Leslie," explains Ferguson, adding that they were introduced several years ago by a mutual friend who knew they would bond. Immediately, Ferguson recognised that Ash was not the blonde bimbo portrayed by the tabloids as trapped in an abusive relationship with a violent man. In fact, the couple celebrated their 20th wedding anniversary in LA earlier this month. "He's been amazing, has my Lee," says Ash. "Unbelievable! I don't think either of us knew he had it in him to become such a brilliant carer.

"He's supported me at every turn and is still very over-protective. I'd say he was my rock, if that didn't sound a bit Paul Burrell." Theirs was always a turbulent marriage, but it's also a love match. She and her older sister Debbie, a former Hot Gossip dancer, are estranged, after Debbie alleged Lee had been violent towards her sister. Even their father Maurice's death didn't bring the sisters together again, as Ash writes in her autobiography, My Life Behaving Badly.

Concerned at the adverse press her friend was receiving in the wake of her near-death experience, Ferguson visited Ash in hospital, taking her a flashing cowboy hat to wear in bed. Ash, a tomboy as a child, had once told Ferguson how her mother had forbidden her from wearing her favourite item of clothing, a Stetson, in bed because she feared it might make her ears stick out.

"You also brought me a comedy pen – a purple bird that the nurses called Mrs Plume, because that was my pseudonym in hospital – and a sparkly notebook, and told me to start writing my own story," Ash reminds her. "So I did and last year I published it."

"I just felt it was all so bloody unfair and irrelevant. An 'unnamed friend' saying this, 'a worried spokesman' saying that. I mean, no-one ever spoke about Leslie's work – and I'm loving your work, lady," Ferguson says, giving Ash a bear-hug.

"Well, it's the very, very good writing," responds Ash. "Lynn did all the work on the Bliog."

Ferguson explodes: "That's s***e, Les. I wrote this piece because I think that people always think of you in a visual way and haven't really thought about what goes on in here – your head. Les's really smart. I'm not going to do the 'Leslie's magic' stuff, 'she can wear necklaces', but she's a clever woman. I felt there was so much snobbery about her and it made me furious."

"Well, you know, I am a very, very vain person," says Ash. "I sometimes think all I'll be able to do now is radio, although I do love doing it. I did a play of Lynn's, Goldilocks, for Woman's Hour just after I got back on my feet and I loved it."

The problem is, she doesn't know where she fits in any more. "I enjoy my life. It's so much slower. I go to the gym and I keep myself fit. I love being at home in Fulham with Lee, although my two boys don't need looking after any more – apart from the odd lift. But I think I'm still wandering around not knowing what I'm meant to be doing with my life, so Lynn's Bliog came at a good time."

The two friends often hang out together. "I bring Lachlan to Les's when I write, and this is how crazy my life is, Leslie Ash – of all people! – babysits for me."

Everything about her own life appears to have been exposed by the media, Ash says. "I've tried to put my side across but that's seen as selling out. So I've said to myself, 'Shut the f*** up'. I don't want to sound as if I'm whingeing all the time. But handing your life over to someone else is a strange thing. However, Lynn's so observant. She's really 'got' me."

Certainly, it's impossible to ignore Ferguson. And it will be doubly hard to miss her in Edinburgh next month, because she's reprising her Fringe First- winning, one-woman play, Heart and Sole, about a lonely woman who falls in love with a fish, and a new piece, The Plan, co-written with Elly Brewer, in which Death revisits recent fatalities.

"I know! I know! It sounds dead bleak," says Ferguson, who is nervous about the new work. But she has had plenty of performing experience – she was the voice of Mac in the film Chicken Run, has worked at the National Theatre in London, and appeared on TV in everything from medical soap No Angels to police drama The Bill.

Ferguson has herself only recently returned from the States. She and civil servant husband Mark Tweddle and their sons were staying in LA with her mega-famous brother, Craig Ferguson, host of CBS's The Late Late Show. She was a guest on the programme, with Ewan McGregor and Jackie Chan, so wowing the producers that she has an open invitation to return. "Craig's still just my big brother – but with pots of money," she says.

Although Ferguson is a laugh a minute, she has a thoughtful side, too. She was inspired to write Heart and Sole when her mother – "a lovely, lively, vivacious, nippy woman" – was diagnosed with cancer. "She was unrecognisable, lying in hospital with tubes up her nose and down her throat. I remember thinking that the thing about loving someone is you can't change the way you feel, whatever happens."

Happily, her mother recovered; then her dad died suddenly in 2006. "We've all struggled with our grief because dad was special. I became so depressed that I decided I wouldn't write anything ever again; it was all so bloody pointless. Then Elly and I came up with The Plan and I've enjoyed writing it, even if it is about death and dying – but, hey, it's got laughs, too."

"Well," interjects Ash. "You have to laugh at yourself, don't you? And, honestly, I'm OK. I wish I could wear high heels but I'm very lucky to be on two legs. I really am OK, whatever the tabloids may say to the contrary."

My Life Behaving Badly is published by Orion, priced 8.99. Visit www.bliogs.com to download Bliographies. Heart and Sole and The Plan are at the Gilded Balloon, Teviot, Bristo Square, Edinburgh, 30 July - 25 August. Tickets cost 10. Concessions and preview tickets are available for both shows, tel: 0131-668 1633.