Right now, indeed, she interrupts our meeting — taking place on an empty double decker, in a godforsaken garage in Warrington — to demonstrate her prowess. Marching purposefully down the gangway, she bounces up into the driver’s seat, grasps the steering wheel with one hand and turns the ignition with the other. “Oh no! It’s been immobilised!” she says, like a child discovering that the batteries are missing from her favourite toy on Christmas morning.

We’re here today on location for her latest series, Jane Hall. It’s a semi-autobiographical, six-part comedy drama coming later this month on ITV1, based on Wainwright’s own experiences of 18 months in the bus lane back in the Eighties.

At the time, she was a shy English graduate from York University who had already experienced success with a play at the Edinburgh Festival. She arrived in London hoping to find it paved with screenwriting opportunities. “I knew I wanted to be a writer but I didn’t quite know how I was going to achieve it. I was driving buses for want of something better to do.”

Like all good writers, Wainwright has cannibalised her own experience for her art, although it took some 15 years for her to get round to writing Jane Hall. In the interim she worked on The Archers, then on Coronation Street, at a time when it was an incubator for our best screenwriting talent. Subsequently she has written cutting-edge dramas such as At Home with the Braithwaites and Sparkhouse, as well as Bafta-nominated adaptations of The Wife of Bath and The Taming of the Shrew for the BBC. But she had to be persuaded by her script editor to revisit her time on the buses.

“To be honest, that was the one thing that I never really wanted to write about, because it was such a grim job. Even now, all these years later, I still have nightmares that I’m driving the bus but I’ve come off my route and I’m lost.”

Her memories — many of which find their way into the series — are of being a callow, middle-class northern lass in a southern, largely male, working-class environment. “I’ve given Jane (played by one of Wainwright’s favourite actresses, Sarah Smart) exactly the same ‘fish out of water’ characteristics as I had myself.”

It was a baptism of fire. She recounts one vivid incident involving a drunk who boarded her bus in the early hours. “He staggered down the aisle and then tried to climb to the upper deck. But he didn’t make it. As I pulled away he fell straight backwards, landing at the bottom on his head. Two passengers that I asked to stay as witnesses immediately got off. The police turned up and simply threw the man’s inert body into the back of their van. To this day I don’t know whether he lived or died.”

None of this sounds like the stuff of comedy. But, as always in Wainwright’s work, human drama is combined with high jinks and razor-sharp humour. “But life itself is a bit like that, isn’t it?” she says. “And drama should reflect life.” Typically, too, Wainwright gives us some graphic and hilarious sex scenes. The rumpy-pumpy includes a double decker rocking to the gyrations of Michelle (a bored and unhappily married driver, played by Gillian Taylforth) in consort with her young lover, Steve, played by Noel Clarke. “Not that I recall much bonking at the depots where I worked,” she laughs.

Others in the series’ stellar cast include Geraldine James, who plays Jane’s mother. “I modelled her very much on my own. My Mum was thrilled by the choice of actress.”

Less delighted by the project was Wainwright’s husband, Austin, the father of her two small sons, George, 9, and Felix, 7. He sees himself represented in the drama as lovesick Robert (played by Stephen Mangan).

“I did meet Austin at the same time as I was on the buses. He was working in a music shop in the Charing Cross Road and he became a lodger in my house in London. He moved in, just as Robert moves in to Jane’s house. In the drama there’s a love triangle between Jane, Robert and Richard (played by Daniel Lapaine). That didn’t happen in real life.”

In real life, however, Austin, like Robert, comes from a family of Oxford academics. He is, she says, a very private person who enjoys his part-time, low-profile career as a dealer in antiquarian sheet music. “I’ve instinctively drawn him with lots of love and affection. But I think he’ll be uncomfortable with the attention.”

He may well have taken comfort, then, in the delay in showing Jane Hall. Bafflingly, it has been sitting on the shelf at ITV for two years, though Wainwright has never been more in demand. Right now, she is involved in a range of projects, including The Amazing Mrs Pritchard for BBC One, in which Jane Horrocks plays a supermarket manager who becomes Prime Minister, and Bonkers, which explores the subject of suburban sex.

None of the projects, however, is as personal as Jane Hall. It took some persuasion, then, for her to agree to change the title, originally Jane Hall’s Big, Bad Bus Ride Home. “I agreed reluctantly because the whole thing is about a young woman’s journey into the grown-up world. But ITV argued that having ‘bus’ in the title was a turn-off for viewers.”

• Jane Hall is on ITV1 later this month

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