Now registered blind, the bestselling novelist and award-winning playwright can see a little. Whenever she leaves the house she is wheelchair-bound - although the words "bound" and "Townsend" are mutually incompatible. The creator of secret diarist Adrian Mole admits: "I really should have my sunglasses on, but it's a bit strange wearing them around the house, don't you think?"
As befits a woman known for her sparky wit, she has a wardrobe of piratical eye patches instead, bought for her by her 29-year-old interior designer daughter Lizzie, who is in charge of her mother's personal grooming. This also explains the punky plum-coloured streaks in Townsend's chemically enhanced blonde hair, which is swept today into a smart chignon. Lizzie has also recently painted her mother's toenails candy pink.
"There's even an eye patch in this fabric," says Townsend, producing a leopard-skin print cushion from behind her back. Another in black velvet has sequins and jewels, with a jokey, false-eyelashed eye embroidered on it. Despite the rather glamorous Johnny Depp-style effect, however, she hasn't the nerve to go out in it. She gives a merry laugh.
It's what you expect from Townsend, whose latest book is the wickedly satirical Queen Camilla, that she should find humour in her loss of sight.
Yes, it was a cruel blow, she agrees, without a hint of self-pity, for a writer, a woman who has read obsessively all her life (even while giving birth to her children), to wake from a nap one afternoon to find that all she could see was brown haze. "It was as if the room were filled with brown smoke. I thought the house must be on fire," she recalls. "But it seemed weird because I couldn't smell smoke or hear any flames crackling. I groped my way from room to room, up and downstairs, only to discover there was no fire."
Instead she had suffered two haemorrhages at the back of her eyes. "It was due to complications after I was diagnosed with type 2 diabetes when I was 38.
"I guess it was inevitable that I would turn into Mrs McGoo, because I was so reckless with my diabetes - which makes the tiny blood vessels at the back of your eye unstable and weak. Although I was already partially sighted I never expected to lose my sight so fast, that I would not be able to see to read, which was my greatest fear and which still pains me now - that and being completely vulnerable and helpless so that I can never go off on my own ever again, something I used to love doing.
"But, in many respects, I've only myself to blame. I used to keep my blood sugar deliberately high so that when I was working in the rehearsal room, say, on one of my plays, I didn't disturb anyone at quiet moments by unwrapping a Mars bar if I felt I was about to slip into a coma.
"And I was always in a hurry, leaping on to trains as they moved out of the station, running, running everywhere, forever rushing around from one place to another, and that made it difficult to stick to the diabetic routine. But really I was cavalierly ignoring the fact that I had this disease," she says.
"Yes, maybe I was running away from the truth because my optician had warned me what would happen and that he could do nothing to help me."
Townsend's most iconic creation, Adrian Mole, is now almost 36-and-a-quarter (he will return, she promises). She herself is 60-and-a-half and has never enjoyed good health.
Tuberculosis and peritonitis set in after the birth of her third child, her daughter Victoria. As well as being diabetic - the disease runs in the family; her grandmother suffered from it - she had a massive heart attack back in the 1980s. She has various complications from diabetes, such as Charcot's joint, an illness which affects the bones in her legs and feet, hence the wheelchair.
The nerve endings in her feet and fingers have also been destroyed, which means she can't read braille, "or pick up any of the skills blind people learn". Inevitably, there have been spells of dark depression. And there was a lot of anger at her loss of sight. Tears were shed - "once in IKEA, of all places" - but she says it's made her learn to listen properly, especially to classical music, which she's grown to cherish. Her sense of smell is heightened, too - there's lavender in her tangled front garden and sweet-scented plants in the lovely, wild garden behind her big, sun-drenched kitchen.
She shares her Edwardian home - a former vicarage in "the comparatively posh end" of her native Leicester - with her husband of 30 years, Colin Broadway, and the doors are always open to a close extended family that includes sons (two), daughters (two), grandchildren (seven), various in-laws and friends.
Colin is usually around to offer visitors hot beverages and home baking, but he's fitting a new kitchen for Townsend's 84-year-old mother. So she's on her own today, and takes my arm to negotiate her way from the sitting room to the kitchen, at whose vast table she's normally to be found at work.
There is, it seems, no end to Colin's talents and loving patience, for he is her amuensis and Townsend now dictates all her novels to him. She has written 14, which have sold in tens of millions and been translated into 42 languages, as well as eight plays and four screenplays.
Colin also reads to her every day, although she's able to watch television if she puts her face a few inches from the screen. She also has a whizzy magnifying screen on her computer, which she demonstrates for me, and which enables her to read and sign letters, sometimes jokily as "Blinky Townsend".
"My machine's always on the blink, too," she sighs. "Every time it has to be fixed it costs 350." Not that she can't afford it, but as a lifelong socialist and committed republican she's given most of her substantial earnings to charities and causes she believes in. "I haven't made millions. I'm not JK Rowling, but we are very comfortable. We've all we need, so I gave the rest of the money away."
The daughter of a postman, Townsend was a clever, bookish girl who, after a "fantastic" childhood, was pregnant and married by the time she was 18, having fallen in love at first sight with her first husband, Neil, a sheet-metal basher. "At first sight," she laughs cheerfully. "Ha! The irony of it. Well, that's not going to happen again, is it?"
They had two sons, Sean (41) and Daniel (39) and one daughter, Victoria (37), together. The marriage lasted seven years. Neil left her and the children for another woman, causing her "the most unbelievable pain and heartache". When she met strong, silent Colin, who is not a chatterer like her and who only speaks when he has something to say, he was married, too, but after they slept together for the first time, she told him he must tell his wife immediately or she would never see him again, despite the fact that she knew she'd found her soulmate.
"I didn't want another woman to go through what I had been through," she says, adding that Colin's first wife soon married again "much more happily and contentedly". She's reminded of that myth about the two lovers sundered in half who roam the earth until they find each other again. "We're like the two halves of an oyster shell, joined at the hip," she says. "We complete each other in every way."
Colin encouraged Townsend to begin writing seriously, after reading some of her stories. And so Adrian Mole, aged 13 and three-quarters, was born and his brilliantly farcical diaries accepted for publication. They had one daughter together, Lizzie.
Shortly after Lizzie's birth, around 1980, Townsend discovered that she was pregnant again, although she had been told she wouldn't be able to have any more children. She had an abortion. "I already had four children," she says. "I didn't want any more and Adrian Mole had started to happen. I knew I couldn't cope with any more babies. Oh God, there I go, it's the guilt, trying to justify what I did, making my excuses... No, guilt isn't what I felt, rather sadness and, I suppose, an intense curiosity."
Her voice tails off, then she reveals she fell pregnant a second time, so she had another abortion. She was so upset and ashamed that it had happened twice that she was subsequently sterilised. But she's glad she doesn't have six children, she says. In 1997, still feeling ambivalent about abortion, she wrote her fine psychological novel, Ghost Children, in which she tackled a tough set of subjects; the rights of parents, their questionable right to reproduce, and their equally questionable right to refuse to do so.
An intensely moving book telling of innocents mistreated by inadequate parents and, more disturbingly, "ghost children" denied life through abortion, it is, she says, perhaps her least popular book, which was misread by many critics, she feels, as an anti-abortion polemic.
Just before it came out, she knew she would have to tell her children her own secret in case a newspaper discovered it first. "I decided that I would tell them about only the first abortion," she says. She remembers asking them all to come into the kitchen for a family conference. She'd set chairs around the kitchen table. Her four children trooped in; then she and Colin sat down and she realised, with mounting horror, that she had placed seven chairs at the table.
"Honestly, I couldn't believe it. Ghost children! We all sat and looked at the empty chair, the empty place. It was dreadful. I mean, if I had written that scene for a play or a novel, I would never have employed such a clich; it would have been far too predictable. I still can't explain it."
How did her children cope with her news? "They treated it very, very seriously and thoughtfully," she replies. "They gave it the weighty consideration it deserves, because I hope I've brought them up to be kind people. It was much easier later to tell them about the second abortion. But, you know, I'm really glad I haven't got a child of 27, and another of 26. I have my four and they're very, very dear to me."
If Townsend's remaining senses are sharper than ever, her literary vision is if anything even more acute in Queen Camilla, which offers a nightmarish picture of Big Brother Britain, with the Prime Minister, one Jack Barker, having exiled the Royals to a sink-estate in Leicester, hoaching with barking dogs, where Charles tends his tiny organic plot, while Camilla chain smokes. A few doors down, the Queen is hooked on Emmerdale, worried that she can't find an NHS dentist.
The Prime Minister has passed liberal euthanasia laws to alleviate the pensions crisis and is planning to bring back dog licenses at a cost of 500. Townsend, who is hooked on news and politics, and "obsessed" with Blair, says of Queen Camilla's critique of Blair's Britain, "I think writers are like detectives. We tap into what's happening in the world, the blindingly obvious, I suppose - God, what a phrase to use!"
"Words are very important to me as a writer. People underestimate the power of words and Blair's a glib-tongued lawyer with a clever choice of words. They truly are words of mass distraction. I watch him on TV, my face against the screen. All I can see is his skull-like head, but he's a man being eaten up by what he's done. It will haunt him for ever; it's Shakespearean."
Sometimes, she concludes, with a throaty laugh, when life is nothing but a blur, it has its advantages. "You see things much more clearly."
• Queen Camilla, by Sue Townsend, is published by Michael Joseph, priced 18.99.