The latest work by AL Kennedy, Scotland's only Costa Prize-winning comedian, is a collection of blogs and essays entitled On Writing.

As is soon apparent, however, it might equally have been titled On The Road because, as Kennedy's regular updates on her literary life demonstrate, the modern writer's career is not unlike that of a door-to-door salesman. Good for one's geography it might be; peaceful and static it ain't. Quite where she finds the time and energy to write is only one of the mysteries behind this chatty and discursive series of pieces.

In person, Kennedy, 47, embodies both qualities. Droll and whimsical, she frequently unleashes a wild digression that never forgets to return to base. She is wandering along a London street when I phone her, in search of a quiet café where we can talk, carrying a bespoke blue pinstriped suit she has just collected from her Soho tailor, John Pearse. She will be wearing this, she says, when she appears at Aye Write!

"A trouser suit?" I ask.

"Nobody I care about has ever insisted I should be in a skirt," she replies, in what could be the opening sentence of a short story.

One of Britain's most fêted novelists and short story writers, whose last novel, Day, won the Costa Award and whose powerful earlier novels were also highly acclaimed, Kennedy recently moved from Glasgow to London where, she tells me, it is easier to pick up "small bits of work".

"London's the most parochial place in the world," she says, as a motorbike screams past. "People in Camden won't go to something that isn't in Camden, let alone [go to] Manchester, so if you're there you kind of exist for them in a way that's quite cute and also slightly terrifying, because they're in charge of so much and yet they've got this tiny world."

In a relationship with someone she refers to only as "the gentleman of my choice", she sounds contented and relaxed. This may of course be because she has just had a two-week holiday, something of a rarity for a woman with such a punishing work ethic she makes bees look like sloths.

She mentions that a few weeks ago she fainted while she was giving a reading. "That was a first," she comments drily. "I said to the audience, 'I'll just sit down a bit, I feel a bit weird.'" Aware that she couldn't see the words on the page, she then told them, "I'll just go and run my head under a tap." Those in the front row told her not to come back as she was clearly unwell.

"And then I went downstairs and crumpled up in a heap. And they got the ambulance man to me, and the only person for whom I signed a book was the ambulance man. Once he found out I wasn't dying and had done the EEG and all that stuff, we had a strange discussion about literature in the ambulance."

That, in a nutshell, is the writer's life as On Writing describes it. It is exhausting, unrelenting, makes one ill, and can only be justified by a compulsion to write, and to meet one's readers, that is just this side of barmy.

So, as Kennedy walks past a Texaco garage while being tailed by a wailing police car, I ask if On Writing was compiled as a self-help guide for would-be writers, or more of a cautionary tale.

"Partly it was to say, 'This is the industrial thing which goes on behind what you're reading'," she says, "but it's more to be company. There's not an awful lot that you can do to help - The things you can do, like say, 'Go away and do this exercise', aren't really helping, because one of the scariest things about writing is that you have to sit there and generate an idea, and deal with your head being apparently empty. And if I say, 'Write about cabbage', it's not helping, because you have to find your own cabbage."

As for the manic travelling, she makes it clear how unenviable this part of the job can be. "It is difficult. I'm a lucky writer because I earn my living, but in order to earn your living and not do things that you find morally uncomfortable, you have to work. And a lot of it now does involve travel."

She raises her voice above the pounding of a jackhammer drill. "You want to be published in Europe, and you want to be published in America, and so you really have to go there. Which sounds like a high-flier's problem, but if you're really knackered and you're only going to see a hotel in somewhere potentially quite dodgy, it's not necessarily the most fun you can have.

"I've just been up to see my godchildren. I haven't seen them for a year. It's quite literally heartbreaking. You don't get to see the people you care about. It's blooming horrible."

The traffic and power tools quieten at last as Kennedy finds a café. The only noise now is the gushing of a cappuccino-maker and the buzz of a caffeinated crowd. While she orders a chai latte and finds an empty table, she continues to talk without pause, a skill no doubt honed by years of stand-up comedy, where to hesitate or falter is to invite trouble.

So, of all the comments she offers in On Writing, what is the best single piece of advice she can give a new writer?

"Oh, I think the thing that my grandfather told me – address whatever you're afraid of. There will be things that you're afraid of writing, and those will be precisely the things that you probably should write about, and it won't kill you, and it will only come up when you're ready. Your brain sort of self-governs. It will not provide you with something you can't handle.

"You've got to trust yourself and then it won't hurt you. Some writers will ration things – 'I'm saving the excitement for the end' – and you say, 'I'm sorry to tell you but the excitement has to be all the way through, and just more at the end.' Which is demanding, but it means you will find out how to make excitement, as opposed to assuming you don't know how to make excitement and you can only have one exciting thing happen and it will be on page 300, by which time all of your readers will have left."

Generous with her time, both to fellow writers and readers, I wonder if she is simply being as polite as the next well-brought-up Dundonian would be to the next generation of novelists and her fans?

"I wouldn't want to describe anybody as a fan, it's not that kind of gig," she replies. "If people didn't read me I'd be screwed. There are many genuine ways in which everybody is all in it together. Before the courses and before you had to pay for things, and before you got mentored on an official scheme and you had to pay by the hour, writers helped writers. Writers have always helped writers. We understand it's not an easy thing to do. It's weirdly posh and luxurious and wonderful, but it's also lonely and horrible. You've got to pass it on otherwise it's really toxic, it's bad karma.

"And it's practical as well. If you're sorting out somebody else's problem, it is still keeping your problem-solving equipment in good shape. It's not like your wisdom is going to leave you. It's like happiness; it's not a finite quality. You don't have to make people miserable in order to preserve that happiness."

For the first time in our conversation there's something like silence at the end of the phone. Is everybody in the café eavesdropping? Have the remorseless city noises simply been a recorded backing that has just ended? Is she not in London but Alaska, or a trappist monastery in Tibet? Who knows. With AL Kennedy, anything is possible.

On Writing is published by Cape, £17.99. AL Kennedy appears at Aye Write! on April 19. For more details, go to www.ayewrite.com or for tickets call 0141 353 8000.