Thankfully I'm on time and this is despite getting lost and having to phone her for directions. She offers to come outside and look for me, and so this is how I first see Ruth Rendell: alone on a street overlooking a canal on which narrowboats bob lazily; tiny, trim, with a thick crop of dyed blonde hair and a smile tickling the corners of her mouth. Unsurprisingly for a writer of such unrivalled powers of observation, she has already spotted me.
Rendell is softer, kinder, more cheerful than I imagined. In interviews she is often portrayed as remote and forbidding, and then there's her literary voice (cool, elegant, detached) and her view of the universe (bleak). She tells me she believes the world is "a terrible place, in many ways a vale of tears". Her characters inhabit dark places of inequality and injustice whether that's the fictional market town of Kingsmarkham in her long-running Inspector Wexford detective series, or the sprawling, unforgiving London of her Barbara Vine thrillers. Rendell has a terrifying capacity for psychological insight. She can make us feel empathy for murderers, the people who, in her novels, are often society's victims.
So why does she appear so chipper? She starts laughing and fixes her glittering blue eyes on me. "It's funny because my son said to me recently, 'I wish all these journalists would stop saying you're so dark, because you're not'. People want to make me (that way] because otherwise they can't match me to my books. I would never say that the world is a happy place, because life is wretched for a lot of people and I'm aware of that, but you can hold those views and still have a cheerful, optimistic nature. I can't explain it, but you can."
We make our way downstairs to a large bright room lined with books, where her two cats are snoozing, and French windows open out to a flower-filled garden. She keeps the garden herself and even climbs on to the roof to clean out the gutter, "because no one else is going to do it". It was while doing so that she came up with the idea for one of her Barbara Vine books, Grasshopper, about a gang who trek across London's rooftops. Even when Rendell is pulling leaves from a gutter, her brain is ticking over, hungry for the next plot.
Her appetite for reading is as voracious as it is for writing. She gets through around three books a week. On the table is Wilkie Collins' The Law And The Lady, a novel by Norwegian crime writer Karin Fossum, a history of women after the First World War, and more. Her favourite book is Ford Madox Ford's The Good Soldier, which she has read more than 20 times. She's currently rereading Dickens, and last year devoured all six volumes of The Decline And Fall Of The Roman Empire ("A wonderful experience, and I was quite sorry when I finished, but I can always read them again"). Rendell's conversation is peppered with quotes – a habit she shares with her sleuth, Inspector Wexford – and I get lines from Edgar Allen Poe, Somerset Maugham and George Orwell.
And I can't leave out the book on the table by her good friend PD James, that other redoubtable queen of British crime. James is also a baroness, though she bats for the blue team. "We don't discuss politics and it's never got in the way," says Rendell. "We share a taxi home from the Lords and pass each other in the chamber and embrace, much to the amazement and consternation of everybody."
Her 13th Barbara Vine novel, The Birthday Present, is a political thriller set in the early Nineties about the fall of a rising Tory MP. It revolves around an adventure sex game that goes wrong, and Rendell relished writing it. "Somebody I met at a party told me about adventure sex," she says. "He found it shocking, and I thought, 'well I rather like that'." This reminds me of what her friend Jeanette Winterson has said about her: "She has a truly open mind and will think about whatever you put to her. Nothing would shock her. She is genuinely free of prejudice."
Rendell's first Vine novel came out in 1986, when she had an idea that wouldn't fit either of her categories of police procedural (the Wexford series) or psychological crime. She decided to write it using her middle name and her great-grandmother's maiden name, and so Barbara Vine was born. In fact she was always called 'Ruth' by her father's side, and 'Barbara' by her mother's, but now has just one family member left who calls her 'Barbara'.
She is extremely regimented and rises every morning at 5.30am, writes from 8.30am till lunch, then walks to the House of Lords. "It would be hard for writing to be as enjoyable as it was when I first began because that was a very intense pleasure," she admits. "But I can't imagine not writing, I'll say that. It doesn't get any easier. I think I'm more exacting about what I do, more fussy, more particular. I would like it to be better all the time."
Her first book, From Doon With Death, for which she was paid 75, was published in 1964. "I bought my husband a watch (with the money]," she says. "I bought bed linen and a lamp, but I can't remember what I did with the rest. I don't think I bought anything specifically for me, which goes to show what a noble nature I have." She laughs.
Her husband died almost 10 years ago, and she still misses him greatly, "though that is the lot of many people". They married when she was 20 but divorced for a brief spell in the Seventies before getting back together. "On either side of our divorce we were together for a long time. It is a wrench, a great wrench."
Within a month of his death, Rendell started writing again. Did it feel different writing about death and bereavement after experiencing it so intensely? "I don't think so. I'd lost friends, I'd lost my parents. I think one has some idea what it feels like…" She pauses, then changes her mind. "I think it did affect how I wrote, yes, now that you mention it. That awful feeling that lasts for a long time when you're always expecting the person to be there, to walk into a room, I didn't realise it would be like that, and yes I did use it." She won't live with anyone else, and doesn't get lonely.
"I feel old and I don't mind it," she says, which is probably what keeps her looking 10 years younger than she is. "I think it's ridiculous when people my age say they don't feel any different. I have all these years of life behind me – of course I feel old." She enjoys witnessing how attitudes to women have changed, going in to get her car serviced and "being treated just as if I were a young man. I'm glad I've seen that happen."
Many would say the greatest crime is that Rendell has never won the Booker. For almost half a century she has written three books every two years, creating along the way a compelling and rigorous document of modern Britain.
This, it turns out, is what she values most. "People ask me what I want to be remembered for and I don't really care," she says. "But if it's for anything it would be the idea that people can go to my work – if it lasts – and find out exactly what it was like in 2008. I hope for that."
Barbara Vine, The Birthday Present, Viking, 18.99